Microscopic investigations of thinly cut fixed tissue sections and living cells adhered to glass substrates routinely produce superb high-resolution images when employing plan apochromat or fluorite objectives having a high numerical aperture. However, a significant amount of current biological research involves the investigation of cellular dynamics inside living tissue where important events can occur deep within the specimen, far away from the cover glass. Attempts to image cellular details and activities at a micrometer distances from the specimen cover glass with conventional oil immersion techniques often suffer from artifacts, including severe optical (spherical) aberration. The use of water in place of oil, as the immersion medium, is an effective approach to overcoming the aberration problems, and highly corrected water immersion objectives have been introduced by several manufacturers for applications involving living cells and tissues.
Recent technological advances in instrumentation and software systems, coupled to the development of new fluorochrome probes, have combined to significantly advance the frontiers of knowledge in living cell and tissue studies. The primary optical and quantitative imaging techniques utilized for these investigations include confocal and multiphoton microscopy, differential interference contrast (DIC), and traditional widefield epi-fluorescence methods. A fundamental issue in living cell studies is that proper maintenance requires the cells be surrounded in a chamber or vessel with an appropriate nutrient physiological solution, and regions or events of interest are often located 50 to more than 200 micrometers away from the cover glass. Several investigators have discussed the limitations of employing high numerical-aperture oil immersion objectives for imaging focal planes that are not immediately adjacent to the cover glass. The most severe deficiencies identified are reduced resolution and image intensity, and these artifacts become significant at distances from the cover glass of more than approximately 15 micrometers. Spherical aberration caused by the mismatch of refractive indices in the optical path is the primary cause of the image deterioration, and this aberration increases proportionally with imaging depth.
The primary rational for utilization of immersion fluids is to realize the maximum numerical aperture of the objective, providing improved diffraction-limited spatial resolution. However, a more practical advantage is that the occurrence of spherical aberration is made less likely. Because of the typical refractive index of optical glass employed for microscope objectives, the highest ultimate optical performance is currently provided by oil immersion objectives. Under ideal imaging conditions, the best optical performance is achieved by use of immersion oil that exactly matches the refractive index of the objective front lens element and cover glass. Substitution of water or another immersion medium having a higher or lower refractive index degrades this performance. However, in situations that are non-ideal, in which spherical aberration becomes the limiting factor for image quality, the use of lower-index immersion fluids can often be advantageous. Introduction of aqueous media into the optical path of an oil immersion system increases spherical aberration, and the benefits achieved by employing a water immersion objective result simply from reduction of the most significant and limiting aberration under the prevailing imaging conditions.
Theoretical Optical Considerations
One of the most widely employed methodologies in living cell and tissue research is conventional widefield fluorescence microscopy, in which high numerical-aperture oil immersion objectives are used to observe relatively flat specimens immediately adjacent to the cover glass. Fixed tissue sections or cells are embedded in an aqueous medium having a different (lower) refractive index than that of the cover glass. Light exiting the objective traverses the immersion oil and the cover glass (which by design have the same refractive index), and is refracted upon encountering the interface with the embedding medium, having a different refractive index. The net effect of the light deviation at the refractive-index interface depends upon the depth of the observation plane. At focal planes near the cover glass, the objective optical design requirements are met, and the system performs quite well.
The introduction and development of techniques such as confocal and multiphoton microscopy has altered imaging requirements from the conventional situation by enabling study of much thicker specimens, and the three-dimensional visualization of large specimen volumes, often involving some form of image deconvolution or reconstruction. The ability to image optical sections at large depths within a specimen, far removed from contact with the cover glass, changes the optical properties of the system in that the light traverses a medium that was not intended by design. Optical correction is optimized for the light distribution in a homogeneous medium adjacent to the cover glass, although in practice, the observation volume may be some distance away, and the distribution of light is dramatically affected by refractive index differences and by the distance of the focal plane from the glass. The resulting deviations cause a loss of resolution and signal intensity, and a focus shift. The reduction in resolution and image brightness that occurs in many instances when the plane of observation is moved from the specimen-glass interface to deeper regions in the specimen was noted in the mid-1980s by Stefan W. Hell and others, and became the subject of much research aimed at interpretation of the confocal fluorescence image.
Illustrated in Figure 2 are the comparative optical situations for which the oil immersion objective functions ideally (Figure 2(a)), and for which a refractive index mismatch between the immersion oil and an aqueous medium results in serious image aberrations (Figure 2(b)). Imaging a specimen plane that is separated from the cover glass by a region of aqueous medium is representative of the optical conditions that prevail in thick biological specimen studies, and the image deterioration encountered is a primary incentive for the employment of water immersion objectives.
The ideal optical situation for employment of a plan apochromat oil immersion objective is established when the specimen is in direct contact with the cover glass, ensuring a homogeneous refractive index (nominally 1.515) throughout the light path from the focal point at the surface of the specimen, through the cover glass, into the immersion oil, and continuing into the front element of the objective. In this configuration (Figure 2(a)), no refraction of the light waves occurs and the full numerical aperture of the objective is utilized. Furthermore, lens aberrations are well controlled and the resulting images exhibit maximum resolution and contrast.
As the focal plane is adjusted toward deeper regions within the cell or tissue section, or if the specimen lies beneath a layer of physiological medium, the light path traverses refractive index interfaces or gradients between the specimen (n = 1.35), the aqueous physiological saline solution (n = 1.33), and the cover glass-immersion oil-objective combination (n = 1.515). Refraction of the light rays occurs at each refractive index interface, with the result that the full numerical aperture of the objective is not realized, and optical aberrations are introduced as the objective departs from its design criteria. Refraction causes bending of the light rays toward the optical axis as they pass from the aqueous medium into the higher-refractive-index glass, effectively limiting the maximum numerical aperture of the objective (see Figure 2(b)). Introduction of water into the light path of an oil immersion system utilizing a 1.4 numerical-aperture objective, for example, reduces the effective numerical aperture to a maximum value of 1.33. The oil immersion objective cannot meet its design performance when a specimen is viewed through a layer of water or physiological medium, and the spherical aberration introduced results in severe adverse effects in the image. These effects increase proportionally with depth in the specimen, as the distance of the focal point becomes farther from the lower surface of the cover glass.
In studies involving the imaging of living cells utilizing oil immersion, spherical aberration becomes a limiting factor in image quality. The proportional increase of the aberration with imaging depth in the cellular material or the aqueous media surrounding the cells manifests itself as diminished intensity and contrast that prevents the resolution of smaller specimen details. It has been experimentally demonstrated that the effects of this distortion are sufficient to cause misinterpretation of specimen structures such as cilia in marine organisms. The application of deconvolution methods to mathematically compensate for distortions of this nature is one possible solution, although accurate measurements of the point spread function (PSF) are necessary, and accomplishing this becomes problematic when the point spread function is distorted axially as well as transversely.
In all of the methods of three-dimensional microscopy, which are increasingly being applied in investigations of living cells and other non-embedded biological specimens, aberrations in the point spread function are significant because of the relatively low refractive index of the specimens. Point spread function distortions can have particular significance in confocal microscopy since the spherical aberration that is induced impairs the very abilities that are the primary advantages of confocal microscopy: elimination of out-of-focus information to increase contrast and effective resolution in the x-y plane, and the creation of high resolution x-y-z optical sections. To the extent that refractive index mismatch is the cause of image aberrations, the employment of water immersion objectives should greatly enhance high-resolution depth dependent imaging of low refractive index specimens.
In microscopy of a three-dimensional specimen, the image data may be considered a representation of the specimen that contains aberrations, or has been blurred, by the three-dimensional point spread function. If deconvolution methods are to be utilized to reconstruct the object from the aberrant image data, an accurate determination of the point spread function is required. Both direct measurement and computational approaches are employed to describe the point spread function, and each technique has advantages and disadvantages. When experimental comparison is made of data acquired with an oil immersion system and with water immersion, using either measured or computed three-dimensional point spread functions, focal plane-dependent spherical aberration is markedly reduced in the water immersion system.
A comparison of imaging ray traces that occur between the specimen and immersion objectives (both oil and water) is presented in Figure 3, along with a geometric model prediction of an x-z image for a fluorescent bead 100 micrometers below the interface in aqueous media. In Figure 3(a), the sphere on the left represents the actual shape of the fluorescent bead, while the elongated shape on the right is the impression provided by imaging with an oil immersion objective. Ray traces (yellow arrows in Figure 3) from the bead into the front lens of an oil immersion objective (Figure 3(b)) and water immersion objective (Figure 3(c)) reveal details about how the refractive index mismatch obscures actual specimen geometry. In aqueous media, the bead is distorted into an apparent elongated oval when imaged with an oil immersion objective as illustrated in Figure 3(b), but remains spherical when using a water immersion objective (Figure 3(c)). The actual specimens are represented by a blue sphere and the apparent images are indicated as a red oval or red sphere.
In order for three-dimensional image data is to be a reliable representation of the true specimen (convoluted by the point spread function), it must be known that the point spread function does not vary with axial or transverse focus shifts. In practice, this may not be the case if the conditions for which the objective is designed are not met. The objective's design criteria are a function of the refractive indices of specimen, the immersion medium, and the thickness and refractive index of the cover glass. When the refractive index of the specimen and immersion medium match, aberrations are minimized for any specimen thickness, because focusing to deeper planes in the specimen medium combines an increased optical path length in that medium with a compensating reduced path length in the immersion medium. The two effects of the stage displacement offset one another so that the object and image conjugate surfaces of the lens system coincide, as required for image formation without aberrations. The oil immersion objective, therefore, meets the design requirements when utilized to image embedded specimens, but exhibits significant deviation in the point spread function along the optical axis when employed to image low-index biological specimens. In a system in which the point spread function varies axially, the point spread function would have to be computed for each image plane in a three-dimensional stack, requiring a complex model for computing the variance, as well as an image-processing algorithm more powerful than deconvolution. These considerations provide strong justification to utilize water immersion objectives for investigation of three-dimensional biological specimens, in an effort to minimize the axial variance of the point spread function, and the resulting image aberrations.
Design and Performance of Water Immersion Optics
One of the basic functions of any immersion objective, one that requires a fluid other than air between its front lens element and the specimen, is to increase the numerical aperture of the system. In utilizing an oil immersion objective, it initially appears that the thickness of the cover glass would be of little importance, since its refractive index approximately matches that of the immersion fluid. This is essentially true as long as the specimen is mounted in Canada balsam or another medium with refractive index similar to that of the cover glass. When a specimen is mounted in an aqueous medium such as physiological saline, having a refractive index significantly different from that of the glass and immersion oil, the optical performance changes considerably. Consequently, focusing through an aqueous layer even 10 micrometers thick can introduce severe image aberrations, due to asymmetry in the point spread function with respect to the focal plane (see Figures 2 and 3). Unless the specimen region under observation is in direct contact with the cover glass, the optical assumptions utilized to correct the lens aberrations in oil immersion objectives are not valid.
As this behavior of oil immersion objectives became more apparent to investigators, and the limitations imposed on the emerging techniques of three-dimensional imaging in the study of living cells and tissues were recognized, several microscope manufacturers began introducing well-corrected high numerical-aperture water immersion objectives in the mid-1990s. With plan apochromatic correction, and numerical apertures of approximately 1.2, the water immersion objectives have somewhat lower numerical aperture values than the comparable oil immersion lenses, but add the critical capability of allowing high-resolution imaging through aqueous layers on the order of 200-micrometers thickness. Although the principal advantage of water immersion objectives is improved imaging capabilities in thick preparations of low refractive index biological specimens, other practical benefits are derived from the use of water as the immersion fluid. Water has no inherent fluorescence to complicate image interpretation, there is little risk of contaminating physiological solutions, aqueous solutions do not require special cleanup methods, and the cost is negligible.
A highly corrected 60x plan apochromat water immersion objective produced by Nikon was developed with consideration of specifications first suggested by Shinya Inoue, and is representative of similar objectives introduced by other manufacturers. The objective features a 1.2 numerical aperture and a working distance of 220 micrometers, affording it the potential to image focal planes at this depth within a water-borne specimen (see Figure 1). A correction collar allows adjustment to accommodate cover glass thickness ranging from 0.15 to 0.18 millimeters, an essential feature for elimination of spherical aberration. Additionally, the objective exhibits high transmission and chromatic aberration correction from the near ultraviolet through the red visible spectral regions, and therefore can be utilized both for confocal microscopy and for conventional fluorescence and differential interference contrast (DIC) techniques.
As previously discussed, homogeneous immersion would ensure that light rays are not deflected on their path through the specimen and immersion media until reaching the rear surface of the objective's first lens element. If refractive index interfaces are eliminated, an objective can be designed to achieve diffraction-limited performance throughout its entire focusing range. Application of water immersion with low-index specimens eliminates the problem of the higher refractive index with immersion oils, but if the water immersion objective is used with a cover glass, a difference in refractive index between the glass and water is introduced (Figure 2(c)). The exact refractive index and thickness of the cover glass becomes crucial in achieving maximum resolution, and is the reason that many water immersion objectives include a correction collar for compensation of varying cover glass properties. Optical plastics may also be useful in reducing refractive index mismatches between the mounting medium and the immersion fluid for water objectives. Plastic cover "glasses" having a refractive index in the range between 1.35 and 1.4 should significantly reduce the refraction angle of imaging light rays that traverse from the specimen to the objective front lens element through an aqueous medium.
Practical evaluation of water immersion objectives has been carried out by a number of investigators, utilizing different means of assessing the benefits of this type of system in certain applications. Based on theoretical considerations on the impact of spherical aberration on point spread function, clear advantages of water immersion over oil immersion techniques for biological studies is predicted, particularly for specimen planes located some distance away from the cover glass. The experimental results have largely supported theoretical predictions, demonstrating significant improvements in the ability to image deep into aqueous specimens, compared to results with oil immersion objectives.
One experimental evaluation of the performance of a 60x water immersion plan apochromat objective of 1.2 numerical aperture, as described above, in comparison to a 60x (1.4 numerical aperture) plan apochromat oil immersion objective, was conducted by imaging a test target and a highly detailed diatom at various distances below the cover glass (see Figure 4). The results were consistent with theoretical predictions: the oil immersion objective produced images with excellent resolution and high contrast only when the test specimens were situated in direct contact with the cover glass, and exhibited severe contrast degradation when the targets were imaged through an 84-micrometer water layer. The water immersion objective produced slightly lower resolution and contrast, compared to the oil immersion objective, when the target specimens were in contact with the cover glass, but the image quality was maintained with essentially no degradation when the water layer was added to the imaging path.
Presented in Figure 4 are central portions of a star test target imaged with a standard 60x apochromat 1.4 numerical aperture oil immersion objective (Figures 4(a) and 4(b)) compared to the results with a 60x apochromat 1.2 numerical aperture water immersion objective (Figures 4(c) and 4(d)). The specimen was prepared either with water (Figures4(b) and 4(d)) or without water (Figures 4(a) and 4(c)) between the cover glass (170 micrometers thickness) and the test target. In Figure 4(a), the target image was captured with the oil immersion objective and no water between the test target and cover glass. The contrast vanishes at a radius of 2.3 micrometers from the center, which corresponds to a spacing of approximately 0.2 micrometers. The central black disk has a diameter of 1.2 micrometers to provide a size reference. When the same objective is utilized to image the target with 84 micrometers of water between the test target and cover glass, the contrast is seriously degraded and spacings below 0.4 micrometer become invisible (Figure 4(b)). In comparison, when the test target is imaged by the water immersion objective with no water between the target and cover glass, the contrast disappears for spacings below 0.24 micrometers (Figure 4(c)). When an 84-micrometer layer of water is placed between the target and the cover glass (similar to the oil immersion objective discussed above), the contrast remains high (Figure 4(d)) and the performance of the water immersion objective is not compromised by the additional water layer between the cover glass and test target.
Quantitative evaluation of the performance of the two objectives is illustrated by graphs of the contrast transfer function for test targets consisting of equally spaced light and dark bars of various spatial frequencies (Figure 5). The contrast transfer graphs illustrate the amount of target contrast (as a percentage) that the optical system is capable of transferring from the target (specimen) to the image. An image that maintains the full contrast of the target for a given spatial frequency would be plotted as 100 percent on the graph, representing perfect contrast transfer by the system. As contrast deteriorates at higher spatial frequencies, it eventually is reduced to zero at a particular line spacing, which can be taken as the absolute limit of resolution for the optical system being evaluated. Each graph illustrates contrast transfer functions produced under several conditions: with no water layer between the cover glass and the test grating, and with different water-layer thickness added. In addition, theoretically calculated contrast transfer functions are plotted for aberration-free objectives of corresponding numerical aperture. Data for up to 153 micrometers of water is presented for the water immersion objective, while 50 micrometers is the maximum water thickness illustrated for the oil immersion objective.
As illustrated in Figure 5, the water immersion objective delivers contrast and resolution values nearly equivalent to the theoretical limits, and maintains its performance when water layers of 80 and 153 micrometers are added between the target specimen and coverslip, a simulation of the situation encountered in imaging deep within aqueous material such as living cells or tissue. In contrast, the oil immersion objective exhibited a 50 percent reduction in resolution limit, and severe degradation in contrast when tested with only 50 micrometers of water overlying the target. The performance declines steeply with increasing spatial frequency.
Additional evaluation has demonstrated the ability of the high numerical-aperture plan apochromatic water immersion objective to obtain high quality images at a depth of 220 micrometers in water, a feat that would simply not be possible using an oil immersion objective. Other investigations have performed measurements of the water immersion objective point spread function, which support the test target performance reported, and further illustrate the benefits of improved symmetry of the function above and below the plane of focus. The measurements demonstrate that depth-dependent distortion can be modeled and corrected, enabling the lens to be used for accurate measurements along the z-axis for determination of vertical resolution. The fact that the point spread function of the objective is symmetrical above and below the focal plane (indicating minimal spherical aberration) allows it to match the theoretical axial resolution calculated for an objective of its numerical aperture. One overall benefit of this optical performance is a significant improvement in image deconvolution methods applied to three-dimensional specimens, as compared to the same techniques utilizing oil immersion objectives. Furthermore, the essential elimination of spherical aberration in the water immersion objective results in improved signal collection and image brightness when imaging at depths of more than approximately 20 micrometers in aqueous media or tissue.
Special Aspects of Confocal Microscopy
Principal benefits of confocal methods include controlled restriction of the focal plane thickness to allow optical sectioning, and improved resolution and contrast by elimination of flare from signals arising outside the image plane. These two factors combine to permit x-zscan images that provide three-dimensional representations of thick specimens. Spherical aberration limits these capabilities, and increases proportionally with depth in the specimen when the refractive index of the specimen differs from that of the immersion fluid. If an oil immersion objective is used with an aqueous specimen, approximately one-third-wave spherical aberration is added for every micrometer focus depth below the cover glass. Small amounts of spherical aberration cause an expansion of the point spread function and an equivalent loss in axial resolution (see Figure 6). The large degree of aberration that accumulates if focusing beyond about 10 micrometers into a low-index specimen produce considerable blurring of the point spread function and loss of contrast in the image. If spherical aberration is not eliminated, sharpness and contrast losses override any benefit in the confocal approach when imaging at depths of more than approximately 15 micrometers from the cover glass. The utilization of water immersion objectives offers substantial benefits in elimination of these problems when imaging aqueous specimens such as live cells.
Spherical aberration resulting from mismatched refractive indices can distort optical data to the extent that morphological misinterpretation and errors in dimension measurement can occur. The well-known distortion of specimens in three-dimensional microscopy manifests itself as an elongation of features along the optical axis (z-axis). A number of techniques have been employed to measure and to computationally simulate the effect, but contradictions exist over both the magnitude and exact cause. The artifact has been experimentally verified, however, and is known to produce an axial elongation of an object causing it to appear to be up to three times its actual size (Figure 3). The anomaly depends upon the immersion conditions, and is thought to be caused by the fact that axial stage movements do not result in a direct equivalent displacement of the focal position. Errors in the estimation of distances and volumes occur, having major implications in all forms of three-dimensional quantitative microscopy. Among the factors that have been demonstrated to play a role in the distortion effect are the refractive index mismatch between the embedding or surrounding medium and the immersion fluid, the specimen size, the distance from the cover glass, and the numerical aperture of the objective. Utilization of water immersion when imaging low-index specimens such as biological material will lessen the effect, although under some conditions it will not be completely eliminated. Cellular material typically varies in refractive index between about 1.33 and 1.39, and consequently some refractive index mismatch may still exist, even when water is used as the immersion medium.
In addition to dimensional scaling errors when a refractive index mismatch occurs, a significant effect on signal intensity can be induced by the same distortions of the point spread function. In many confocal system configurations, the illuminating pinhole that is scanned across the specimen is utilized in the detection path as well, being scanned by the same mechanism with the purpose of excluding all out-of-focus light from the detector. When imaging deep within a specimen utilizing oil immersion objectives, the severity of spherical aberration can cause sufficient focus shift that much of the light emitted by the fluorophores in the specimen cannot pass through the pinhole to the detector. Therefore, most of the emitted signal from regions of the specimen removed from the cover glass is lost before reaching the confocal detector. The focus shift induced by the spherical aberration is accompanied by a loss of intensity in the acquired image, and the decrease continues geometrically with distance into the specimen.
Published theoretical and experimental analyses confirm that when a 1.3-numerical aperture oil immersion objective is used, imaging a fluorescent plane 20-micrometers deep within an aqueous medium results in a detected peak intensity that is 40 percent less than that from a plane at 10-micrometer depth. This concept is illustrated in Figure 6, which displays contour plots of the confocal point spread functions of a high numerical aperture oil immersion objective, and their respective axial responses for several imaging depths in water. The ideal point spread function (no spherical aberration) is presented in Figure 6(a), while those for imaging depths of 5, 10, 15, and 20 micrometers into aqueous media are illustrated in Figures 6(b)-6(e), respectively. Reduction or elimination of spherical aberration through application of a high numerical-aperture water immersion objective is an effective approach to maintaining adequate signal level in high-resolution fluorescence microscopy.
One often-overlooked advantage of using water immersion objectives in confocal techniques is that water is much less viscous than most immersion oils, and consequently exerts less force (surface tension) on the cover glass during focusing, when the objective and specimen preparation are displaced relative to each other. The cover glass is, therefore, less likely to flex and possibly displace the specimen when focus is changed during acquisition of a confocal z-series. Minimizing specimen movement during the repeated refocusing that is required during optical sectioning can result in sharper and more meaningful three-dimensional reconstructions from the image stack.
Recently, water immersion objectives have been experimentally demonstrated to be suitable for multiple-objective techniques such as 4Pi confocal microscopy and theta microscopy. The axial resolution achieved in 4Pi confocal microscopy is similar to that of near-field optical techniques, and is accomplished by the combination of coherent focused spherical wave fronts from two opposing high-aperture objectives. The coherent addition of two spherical wave fronts results in increased aperture along the optical axis, and a narrower point spread function minimum. This technique has produced the highest three-dimensional far-field resolution obtained to date, which is on the order of 100 nanometers in combination with image reconstruction.
Prior to the development of high-numerical aperture water immersion objectives, the reliance on oil immersion had limited 4Pi confocal microscopy to glycerol-mounted specimens. The refractive index of glycerol (1.47) is sufficiently close to that of immersion oil (1.51), so that minimal compensation is required for the phase shift during axial scanning. A large portion of cellular studies involve glycerol-based mounting media, and at least one manufacturer has developed a high numerical-aperture glycerol immersion objective to minimize the degradation of data resulting from the oil-glycerol refractive index mismatch. Designed for use with a quartz cover glass (refractive index 1.46), the lens incorporates an aberration correction collar that accommodates glycerol concentrations between 72 and 88 percent. This objective has been successfully applied in three-dimensional fluorescence microscopy, and should simplify 4Pi microscopy of glycerol-mounted specimens.
In the case of imaging at depth into water or physiological solution, however, severe spherical aberration and phase shifts do not allow 4Pi microscopy to be carried out with oil immersion or glycerol immersion objectives. Consequently, oil-immersion 4Pi methods are not applicable to live cell imaging. The high-aperture water immersion objectives developed to minimize the spherical aberration induced by refractive-index-mismatch distortions in conventional confocal and multiphoton imaging offer the same advantages in 4Pi methods applied to live cell studies. Although the water immersion objectives have lower numerical aperture than comparable oil immersion lenses, several studies have demonstrated that they produce favorable point spread function characteristics, which allow a fundamental improvement of axial resolution in three-dimensional imaging of living specimens utilizing 4Pi microscopy.
The Meandering River: An Overview of the Subgenres of Creative Nonfiction
Sue William Silverman | September 2008
A PHP Error was encountered
Message: DOMDocument::loadHTML(): ID works already defined in Entity, line: 226
Line Number: 23
NOTES | WORKS CITED
...compared to biography or autobiography, an immersion essay or book gives the reader access to a deeper, more emotionally authentic exploration of the author's subject. This isn't a straight, factual recounting as with a journalist's "who, what, when, where, and why" questions either. The immersion writer guides the reader on an emotional as well as a factual journey.
The genre of creative nonfiction is a long river with many moods and currents. And even though it traverses waterscapes as diverse as the Mississippi, the Amazon, and the Nile, there are seven basic forms-or ports of call, if you will-which we might explore. At the head of the river lie the categories of biography and autobiography. From here, we flow on to immersion writing (or other forms of New Journalism) in which the author immerses him- or herself in an experience, before traveling on to memoir, to personal essay (including nature and travel writing), to the meditative essay, and finally spilling into the lyric essay. In brief, then, the river flows from a relatively exterior focus to an intensely interior one, from a focus on actions and events to one on ideas and emotions. While we begin with a fairly straightforward narrative, we end with one that's subverted or fractured. Yet because this river is a continuum, we'll also find that the ports of call are sometimes so close together that it's difficult to tell where one ends and the other begins.
Port of Call #1: Biography
A case could be made that biography and autobiography should not be included in the genre of creative nonfiction; rather, that they are (or should be) strictly nonfiction, in the same tributary as academic and scholarly writing or journalism. However, given the inevitable subjectivity of the author toward his or her subject, as well as the fact that these two forms have such a long literary tradition, it would be difficult to begin our journey elsewhere.
Biography is a fairly consistent, factual rendering of someone's life, usually a chronological account of "first this happened and then this next thing happened." The author is supposed to be objective-although this isn't really possible. While being objective can be a worthy goal, it's a chimera, a necessary fiction. Lawrence Thompson's three-volume biography of Robert Frost is a good example of this subjectivity.
Thompson, Frost's authorized biographer, grew to dislike his subject, and allowed his aversion to become part of the text. Especially in the final volume of the biography, Thompson paints Frost as a man who, among other foibles, sees himself as a poet whose gifts to the world aren't fully appreciated. "He wanted the consultantship (in poetry to the Library of Congress) to be treated as an office in which his views would be listened to by the men who were running the country, and in which he could achieve significant results for his 'cause': poetry, the arts-and (not inconsequentially) his own reputation."1 The quotation marks around cause and the parenthetical insertion of "not inconsequentially," reveal Thompson's real, subjective feelings toward Frost.
More recently, the poet and novelist Jay Parini released his own Frost biography, with its own subjective elements, albeit different from Thompson's. Indeed, according to reviewer Melanie Kirkpatrick, "Parini is a fan of Frost's, and seeks, in Robert Frost: A Life, to dispel the mythos created by Thompson."2 I doubt Parini would disagree with that characterization, even though it suggests he, too, has an agenda.
In an interview with Paul Holler in the online journal Bookslut, Parini talks about his own expansive view of biography:
I make few distinctions between straight biographies and novels. They both are works of fiction. Fiction means "shaping" in Latin. I shape reality in both genres. There are demands that come from the genre itself: You can't really change points of view in a biography, and you can't make things up; but I think these are small considerations, and that in general they both involve creating narratives, and narrative is what I like: telling a story.3
Although Parini doesn't go so far as to actually "make things up," other biographers do. The most famous example is Edmund Morris's Dutch: A Memoir of Ronald Reagan, in which Morris writes himself as a character into scenes where he was not present. Even though the reader knows Morris isn't physically present, nevertheless, wouldn't it be more honest for the author to admit up-front that objectivity is impossible to achieve? Have Morris, on the one hand (by re-imagining events in order to make elements of Reagan's life more immediate), and Parini and Thompson on the other (by having a subjective point of view), subverted the whole notion of nonfiction?
What's real, what's fact-what, in effect, is nonfiction-is a question our metaphorical river runs into again and again.
Port of Call #2: Autobiography
Autobiography is likewise, theoretically at least, a factual retelling of events. Like biography, autobiography is celebrity-driven (Elizabeth Taylor writes an autobiography; Ms. Ordinary Woman writes a memoir), based on one's "life of action," and thus told more historically than impressionistically-unlike a memoir. The "contract" with the reader, as such, is that the historical facts, at least, are true. For example, when President Clinton writes in his autobiography My Life that, after his re-election, the United States stopped enforcing the arms embargo in Bosnia, we believe him. Likewise, when he writes about his Middle Class Bill of Rights, we believe the particulars of the bill. After all, we could check these facts in newspapers. Where facts might be debatable, however, is when Clinton, say, subjectively analyzes the success (or failure) of his policies in order to enhance his presidential legacy.
Unlike biography, autobiography allows some room for personal reflection. In fact, when the private, personal life intrudes upon the public persona, autobiography hovers closer to memoir-for example, when Clinton depicts, albeit in very general terms, his affair with Monica Lewinsky. Yet even as he allows the reader a glimpse of the personal man, the glimpse is just that: there's little reflection or psychological analysis. Instead, he uses generic terms such as "inappropriate encounter" and "selfish stupidity."4 The deepest he explores a connection between the affair and a troubled childhood-which would be a gold mine for a memoirist-is to mention that, by keeping the affair secret, he once again lived parallel lives, much as he had as a teenager when his alcoholic stepfather abused his mother.
Since autobiography relies on a retelling of events as they happened, the Lewinsky affair is merely one stop along the way of the written life. In the paragraph following this relatively brief discussion about the affair, Clinton describes a meeting with Prime Minister Netanyahu. I had an inappropriate encounter with Monica Lewinsky. I met with Netanyahu. I addressed Congress. I flew to Ireland. Autobiography-unlike memoir, as we will see-tends toward both a certain documentary sensibility and a well-defined chronological structure. Also, since the goal of the celebrity autobiographer is usually to place him- or herself in a positive light, it's frequently not a search for moral or emotional truths or psychological insight.
Port of Call #3: Immersion
In the immersion essay or book, the author, as the name implies, immerses him- or herself in an experience typically outside of his or her familiar milieu. Immersion writers use the voice of an engaged participant, one who writes in first person, sets scenes, employs sensory description, and structures the work with an arc-as opposed to the flatter, more linear voice of a journalist who "merely" covers a story.
There are two basic ways to approach the immersion book or essay.
In the first, the author is the protagonist, thus maintaining a strong, consistent "I" throughout, as in Barbara Ehrenreich's Nickel and Dimed: On (Not) Getting by in America. Ehrenreich investigates how the working class survives on the minimum wage, or worse. Rather than rely on interviews, research, labor reports and statistics-as a journalist would-she herself works such low-paying jobs as waitress and cleaning woman. She is in the story; she's part of it. She writes of her experiences with direct and intimate knowledge.
In the second method, the author also writes in the first-person point of view, but isn't as literally a participant in the story. Instead, the author deals with a broader context or more distant experience. For example, in King Leopold's Ghost: A Story of Greed, Terror, and Heroism in Colonial Africa, Adam Hochschild obviously couldn't participate in colonial events that subjugated the Belgian Congo. Nevertheless, through documents, research, interviews, and trips to the area, he immerses his emotional and psychic self into the events as much as possible. He writes with a clearly subjective regard for the events, as opposed to the dispassionate voice of an academic or journalist, or the more objective view of a biographer. Hear his voice when he first learns of the Congo's "killing fields" in a book he just happened to be reading: "Why were these deaths not mentioned in the standard litany of...horrors? And why had I never heard of them? I had been writing about human rights for years."5 It was an "atrocious scandal," Hochschild continues, using language such as "blood spilled in anger" and "torn flesh."6 Just as Ehrenreich empathizes with those who struggle to survive on the minimum wage, Hochschild immerses himself in the terror of King Leopold's reign.
In the following short section from Hochschild's essay "Isle of Flowers, House of Slaves," we see how, through careful selection of detail as well as the first-person point of view, he manages to immerse both himself and the reader in the action.
These days few spots are purely in the Third World or the First. In Dakar, Senegal, the sun-drenched, crumbling one-time colonial capital of French West Africa, bits of Europe are scattered...like an archipelago. The First World islands are sleek (with) high-rise resort hotels.... Virtually all the guests are white. In...bars...a liter bottle of Vittel mineral water costs the equivalent of several days' wages for a Senegalese laborer....
Farther down (the) road, iron fences have gaps in them; coils of barbed wire on top have half rusted away.... As I jog along the road early one morning, men are urinating in the street, getting up after sleeping the night in the ruins of buildings....7
Even though this essay is more about Dakar than about Hochschild (he doesn't refer to himself until the second paragraph, more or less in passing, "(as) I jog along..."), his presence, nevertheless, is felt throughout. He is the guide between these two worlds. His slant on the details reveals as much about his sensibilities as it does about Dakar. It's wrong for some to have so much while others have so little, he implies.
Therefore, compared to biography or auto-biography, an immersion essay or book gives the reader access to a deeper, more emotionally authentic exploration of the author's subject. This isn't a straight, factual recounting as with a journalist's "who, what, when, where, and why" questions either. The immersion writer guides the reader on an emotional as well as a factual journey.
It is also worth noting the distinction between immersion and personal essays. In the latter, authors don't tend to stray far from their own habitats or familiar emotional landscapes. In immersion writing, as shown, the author usually immerses him- or herself in an environment quite distinct from his or her "normal" life: Ehrenreich is not a minimum-wage worker; Hochschild examines the Belgian Congo from the vantage point of another century. One of the early works of New Journalism is Paper Lion: Confessions of a Last-String Quarterback by George Plimpton, who "joined" the Detroit Lions football team to discover what it was like to be a professional football player-and then write about it. In short, unlike the personal essayist (whom we'll explore in a moment), the author immerses him- or herself in "events" solely to write about them.
Port of Call #4: Memoir
Midpoint on our metaphorical river is the memoir, the subgenre most people associate with creative nonfiction, since it most obviously employs many of the same techniques we encounter in fiction: dialogue, setting, character development, plot, and metaphor. In the forms already explored, the text generally follows a relatively straightforward, chronological recounting of events; here, however, the story begins to find a more personal, emotional arc to follow. Unlike biography and autobiography, a memoir isn't about a whole life but, rather, one aspect of it. It's imperative that the author establish her, or his, clearly defined theme and focus.
What also distinguishes memoir from autobiography is the use of at least two "voices" to tell the story, to explore the depth of events: one I call an "innocent" voice, the other an "experienced" voice-to borrow from William Blake.
The innocent voice relates the facts of the story, the surface subject, the action-not altogether unlike autobiography. It conveys the experience of the relatively unaware persona the author was when the events actually happened. Whether the events are loosely connected by chronology or not, this voice gives the story a sense of "this happened, and then this happened, and then this next thing happened." It is the action, the external part of the story.
The experienced voice, on the other hand, plunges us deeper into the story by employing metaphor, irony, and reflection to reveal the author's progression of thought and emotion. It reveals what the facts mean, both intellectually and emotionally. Reflection is not just looking back, recollecting, or remembering the past. It's a search to see past events or relationships in a new light. The experienced voice conveys a more complex viewpoint, one that interprets and reflects upon the surface subject.
Whether the memoir is essay- or book-length, both voices are crucial: One thrusts the story forward; the other plunges the reader into the real heart of the matter. As these voices intersect throughout the memoir, the author reveals the true nature of the journey.
Lisa D. Chavez's essay, "Independence Day, Manley Hot Springs, Alaska," begins with the innocent voice-the narrator describing how, in 1975, she and her mother depart southern California for Alaska seeking a new life. This voice describes the wonders of Manley Hot Springs as seen through the eyes of a twelve-year-old girl:
Instantly I am occupied, walking our dog, wetting the toes of my canvas tennis shoes in the silty current, kicking sprays of gravel into the air. I narrate the scene to myself, add it to the elaborate and constant story I whisper of my adventures in Alaska.8
Interspersed with the ongoing story is the experienced voice, the adult author-persona who now understands: "I do not see what is in front of me: a shabby small town where people stare openly at that frivolous car-bright orange and marked by its out-of-state plates-and the young woman in white, high-heeled sandals and her daughter that have emerged from it."9 In addition to the "experienced" voice that can describe the car as "frivolous," Chavez employs subtle metaphorical imagery here as well. By including the detail of the bright orange car, she implicitly compares it to the clothing hunters wear. However, as she goes on to show, she is the hunted, not the hunter. She is, as she so accurately says, "marked." She, like the car, is the other.
This is clearly revealed when the narrator's young self experiences racial hatred. Late one evening, Lisa's mother asks her to walk the dog, and as she leaves their rented room above a bar, she is confronted by a man on the landing pointing a gun at her. "'I told all you goddamn Indians to get the fuck out of my bar,' he says."10
In the following paragraphs, the two voices twine together, the innocent voice narrating how she escapes the man, and the experienced voice reflecting upon the event: "I thought (racism) was something else, people who called black people bad names, people who snickered when they heard my last name. Mexican, they'd sneer...."11 Chavez, the author-narrator, deepens the moment even more: "And now I have been shaken into a world I don't understand, a cold, foreign world, where men I don't know can hate me for the way I look."12 This voice of experience continues to explore her place in the world when she reflects how, in California, her darker skin was envied. There, she even secretly felt "superior." In Alaska, however, "brown skin did not mean beach and health, but it meant something...shameful.... Native.... I would discover how that word could be spit out with as much disgust as any racial slur."13
Because memoir is an examination of self, Chavez's persona at the end of the essay is different from her persona at the beginning. By the end, Chavez comes to understand fear; she sees herself and her world through less innocent eyes. "In just a few years...I would learn to put a name to what was happening to me, and learn to be angry.... Even later, I would learn to mold my anger into something I could use."14
The lessons learned in memoir aren't as evident in autobiography. In autobiography, the author may no longer be president of the United States or a box-office attraction, yet emotionally, he or she hasn't necessarily changed-at least on the page. With rare exceptions, autobiography isn't about exploring the subject's psyche. Memoir is. Autobiography isn't about turning a life into art. Memoir is. The autobiographer justifies "mistakes." The memoirist explores them. The autobiographer focuses on success while the memoirist tries to decipher how or why life events often go wrong. Memoir, therefore, is not a simple narcissistic examination of self-as some critics claim. By employing many of the same techniques as fiction, poetry, and belle lettres, memoir achieves universality.
Also, unlike autobiography, memoir relies almost solely on memory. Memoirists may research old letters, conduct interviews with family members, and examine family documents and photographs, but the reliance on one's subjective perceptions of the past is at the heart of memoir. Whereas autobiography tells the story of "what happened" based on historical facts, memoir examines why it happened, what the story means.
In terms of memoir, the reader understands and accepts this tacit contract that retrieving "facts" from memory is both a selective and subjective business. Yet, at the same time, a reader doesn't "allow" the memoirist to lie or make up facts willy-nilly. As Patricia Hampl says about critics' reactions to memoirs, "...they're so assured that there is a thing called a 'fact' and that it can be found like a lost sock, and that once you've found it that's all you've got to do, state a fact. I think that misrepresents entirely the way the faculty of memory works."15
In short, subjective memory is acceptable, while pure invention isn't.
Port of Call #5: Personal Essay
Whereas memoir is a "slice of a life," the author of a personal essay examines an even slimmer piece of that life or, if you will, a single bend in the river. Personal essays encompass such topics as nature and travel, or social and political issues. Whereas memoir is an exploration of the past, personal essays can explore contemporary-even future-events. Instead of the memoirist's thorough examination of self, soul, or psyche, the personal essayist usually explores one facet of the self within a larger social context.
Memoirs and personal essays do have some things in common, however. In both genres, the author imbues his or her work with a strong personal point of view. In addition, personal essayists, like memoirists, usually don't stray far afield from their own habitats or ways of life. Unlike immersion essayists, who seek to immerse themselves in unfamiliar subject matter, personal essayists tend to write about what they already know well. Annie Dillard, for example, writes about Tinker Creek, close to her home in Virginia, a habitat she knows intimately. Dillard, like many nature writers such as Edward Abbey, Farley Mowat, and Terry Tempest Williams, are already naturalists and environmentalists by inclination.
In her essay "The Molino," Melani Martinez explores her culture, her way of life, by focusing on the molino-a machine that grinds corn for tamales-as the embodiment of her cultural world. We read three long paragraphs about this "grinder in the back of this old worn-down garage turned kitchen"16 before we directly "meet" the narrator herself. We smell and hear the machine and understand its impact on her particular world.
It fills the room with its smell. A burning cloud. A grinding stone. It eats corn.... It gobbles it and changes it to something else. To money, to food, to questions and lifestyles. It prepares children for the rest of what will come.... It is a father. It is a dirty smelly father that works and works and pushes and shoves out the meat of little kernels of corn.17
When the narrator finally appears, we learn it is her father who owns and operates the molino; this is her environment, in which others may live but cannot describe: "I watched it all," she writes. "The lime-covered caldron of boiling nixtamal and the oar he stirred it with were even older than him.... All the food and all the people and time that went by in that little garage kitchen."18 This kitchen is a neighborhood gathering place, where news and gossip are exchanged. In addition, most of the extended family work at the molino, including the author, as a child. "My father subjected (me) to child labor before (I) knew how to spell it."19 By focusing on the molino, Martinez crafts it as a metaphor for the grind of eking out a living in the tamale business in a particular culture and time.
Of course, as Martinez explores the molino and what it represents, we have a strong sense of the author's personal sensibilities: "We (Martinez and her brother) paced the floor of that old garage dreaming of school days as the bottom of our tennis shoes stuck to the grime. Other than the corn, everything was black and filmed with...fat.... It was hot, it was humid, and for us there was no greater hell."20 As in a memoir, therefore, a personal essay reflects upon the author's experiences. Yet, instead of examining solely herself, Martinez allows the molino, as an object and as a metaphor, to reveal the secrets it holds for her family as well as for her culture.
Port of Call #6: Meditative Essay
A meditative essay, as the name suggests, explores or meditates upon an emotion or idea by drawing upon a range of experience. It's a contemplation. Unlike the previous forms, the meditative essay is not necessarily triggered by a specific event. For example, Hochschild's essay begins when he visits Dakar; Chavez's essay starts with the move to Alaska. Such events aren't necessary in meditative essays. Instead, an image or an idea may propel it into being.
There are two ways to approach a meditative essay.
The first way is to examine an idea or emotion by embodying it, making it physical. Let's say someone you love has just died. The loss seems so big that you want to explore the whole notion of "loss"-not just one specific loss. In order to do so, you must discover objects that embody an otherwise abstract emotion. The abstractions must be rendered tangibly. You must discover images or metaphors to embody the ineffable.
The second way to approach a meditative essay is to begin at the opposite end of the spectrum, with the tangible thing itself. But to consider a physical object deeply, one must uncover properties hidden within the object. Consider a jar of peanut butter. You might begin by describing the label. But then, as you continue writing, you will open the jar, tangibly and metaphorically, to discover what's inside. It's like unwrapping a present. What do you find inside? Peanut butter, of course! But to meditate upon an object, you must discover more, something suggested by the object, something that's not just personal experience, rather, some existential or cultural or social or political insight about peanut butter. John Updike does this in his essay "Beer Can," which is a funny, insightful meditation on the often maddeningly, impersonal onslaught of "progress."
Robert Vivian's essay "Light Calling to Other Light" provides another example. It begins with a physical candle, before journeying into the abstract notions of joy and belonging. He writes:
Lately, I have started to push a wide, yellow candle into sunlight.... I move it...to capture the light and to hold it for a while. Then its entire fat body glows from within in a rich, mellow flame, like an improbable Buddha who is dining on the universe. Aglow on the table, it is an homage to light for light's sake.21
By the end, he writes of the metaphorical warmth of a candle holding him "in a calm embrace in the duration of the sun passing from morning into darkness."22 The reader sees that the tangible quality of "light," within the "improbable Buddha," is, metaphorically, the discovery of joy within gloom, which is the theme of this meditation.
In short, the abstract idea needs a tangible body; the tangible object needs a soul. In the meditative essay, we see the ascendancy of the narrative of image over the narrative of action-a trend that has its roots in the personal essay (think of the imagistic metaphor of Martinez's molino). Here it is the image that drives the work, creating meaning and forming the narrative arc.
Port of Call #7: Lyric Essay
In the lyric essay, as in the meditative essay, the writer is not constrained by a narrative of action; the movement is from image to image, not from event to event. Here, the psyche works more in the mode of poets who "let what will stick to them like burrs where they walk in the fields,"23 to quote Robert Frost. (Parini's good poet, not Thompson's bad one.)
In John D'Agata's "Hall of Fame of Us/Hall of Fame of Them," the very arrangement of words on the page suggests poetry:
Ergo the town.
Ergo, also, the fence.
Most of Rachel, Nevada, lives near this fence.
Come dusk, at the Little Ale'Inn, the town gets drunk on talk about the fence.24
The images propel the essay forward, moving from the town, to the fence, to the people, to talk about the fence. The rhythm of this movement, a rhythm created by the short paragraphs and the elliptical storyline, make the essay seem more like verse than prose. In fact, one reason writers use this form is to explore the boundary between essay and lyric poetry. As D'Agata himself writes in the Seneca Review, lyric essays, like poems, "require us to complete their meaning.... The lyric essay doesn't care about figuring out why papa lost the farm, or why mama took to drink. It's more interested in replicating the feeling of that experience."25
In this kind of elliptical writing, not all facts are neatly spelled out, understood, or resolved. The reader is required to fill in the blanks as much as possible while, at the same time, accepting that much will remain mysterious. As with poetry, the reader accepts the emotion of the piece itself as the essential "fact." The accumulation of images forms an emotional whole, if not a traditionally essayistic one.
Toward the Sea
Creative nonfiction is all of the above, and more. Elements of two or more of the subgenres discussed can be combined to create "hybrid" genres as well. In many ways, for example, "The Molino," while at heart a personal essay, also includes elements of memoir in the way the author notes the impact of the molino on her life. At the same time, long passages about the molino itself are reminiscent of a meditative chant.
Myriad experimental structures exist in creative nonfiction as well. For the adventurous, anything goes. Memoirs and essays can be written as montages or mosaics. Harvey Pekar's American Splendor series of "graphic memoirs" helps redefine "comic books," while the film version of his life uses documentary to deconstruct the usual Hollywood cliches. In Nola: A Memoir of Faith, Art, and Madness, Robin Hemley incorporates short stories both by himself and his mother, as well as his sister's letters and artwork, into his own creative nonfiction text.
Pat Mora, in House of Houses, relies on poetic language and magical realism. Reading her work, we feel as if every member of her family, alive and dead, are all present, talking together. Marjane Satrapi, in Persepolis: The Story of a Childhood, tells her story about growing up in Iran during the Islamic Revolution through a series of black-and-white illustrations, while Lawrence Sutin, in A Postcard Memoir, uses postcards, reproduced in the text, as portals into memory.
Waters Ebb and Flow
So, you're in the middle of writing something, but you don't know what. Is it memoir? A meditative piece? "How do I decide," you ask.
Just as bodies of water all have a common element, so does creative nonfiction. As we have seen, the distinctions among these subgenres frequently blur. Therefore, the differences are more in terms of degree than kind. For example, memoirs, personal essays, and meditations can all contain similar elements such as employing one voice that relates the story, twined with another voice deepening it, metaphorically.
Yet, as with water-some being fresh, some salty-there are differences in creative nonfiction. In autobiography, immersion writing, memoirs, and personal narratives, an action drives the work. The arc is that of you, your persona, seeking to understand this action. This kind of essay falls more along an axis of action, a series of events you are following like a map of a river.
In a meditative or lyric essay, on the other hand, an idea or emotion drives the work. You seek to give shape to a thought or idea, making the intangible tangible. These essays fall more along an axis of contemplation, whereby images form a constellation. So while you may not be moving forward in time, you're moving deeper into the metaphorical river.
Whatever port of the river you decide to explore, I hope you'll enjoy the journey.
Sue William Silverman's first memoir, Because I Remember Terror, Father, I Remember You (University of Georgia Press), won the AWP award series in creative nonfiction, and her second memoir is Love Sick: One Woman's Journey Through Sexual Addiction (Norton). Her poetry collection, Hieroglyphics in Neon, was published by Orchises Press. An associate editor of Fourth Genre, she teaches in the MFA in Writing Program at Vermont College of Fine Arts (www.suewilliamsilverman.com).
Thompson, Lawrence. Robert Frost (New York: Henry Holt, 1966), p. 474.
- Kirkpatrick, Melanie. "Robert Frost: A Life." www.Pifmagazine.com, August 1, 1999.
- Holler, Paul. "An Interview with Jay Parini." www.bookslut.com, April, 2006.
- Clinton, Bill. My Life (New York: Vintage Books, 2005), p. 774.
- Hochschild, Adam. King Leopold's Ghost: A Story of Greed, Terror, and Heroism in Colonial Africa. (Boston: Houghton Mifflin, 1998).
- Hochschild, Adam. "Isle of Flowers, House of Slaves." Finding the Trapdoor (Syracuse: University of Syracuse Press, 1997).
- Chavez, Lisa D. "Independence Day, Manley Hot Springs, Alaska." Fourth Genre: Explorations in Nonfiction Spring 2000: 72.
- Ibid., p. 72.
- Ibid., p. 74.
- Ibid., p. 75.
- Ibid., p. 75.
- Ibid., p. 77.
- Ibid., p. 78.
- Hampl, Patricia. "We Were Such a Generation-Memoir, Truthfulness, and History." River Teeth Spring 2004: 129–142.
- Martinez, Melani. "The Molino." Fourth Genre: Explorations in Nonfiction Spring 2005: 1–8.
- Vivian, Robert. "Light Calling to Other Light." Cold Snap as Yearning (Lincoln: University of Nebraska Press, 2001), p. 105.
- Ibid., p. 109.
- Cox, Hyde, and Edward Connery Lathem, eds. Selected Prose of Robert Frost (New York: Collier Books, 1949), p. 20.
- D'Agata, John. "Hall of Fame of Us/Hall of Fame of Them." Fourth Genre: Explorations in Nonfiction Spring 2000: 31–37.
- D'Agata, John. "Finding Love at Thirty." Seneca Review Spring 2000: 5–11.
Dillard, Annie. Pilgrim at Tinker Creek (New York: Harper Perennial, 1998).
- Ehrenreich, Barbara. Nickel and Dimed: On (Not) Getting by in America (New York: Metropolitan Books, 2001).
- Hemley, Robin. Nola: A Memoir of Faith, Art, and Madness (St. Paul: Graywolf, 1998).
- Mora, Pat. House of Houses (Boston: Beacon, 1998).
- Morris, Edmund. Dutch: A Memoir of Ronald Reagan (New York: Random House, 1999).
- Parini, Jay. Robert Frost: A Life (New York: Henry Holt, 1999).
- Pekar, Harvey. American Splendor (New York: Ballantine, 2003).
- Plimpton, George. Paper Lion: Confessions of a Last-String Quarterback (New York: Pocket Books, 1967).
- Satrapi, Marjane. Persepolis: The Story of a Childhood (New York: Pantheon, 2004).
- Sutin, Lawrence. A Postcard Memoir (St. Paul: Graywolf, 2003).