Biomedical subjects

J A Schirillo

Publications and source records attributed to J A Schirillo.

12 recordsLinked to original sources

PubMed2004

Unifying multisensory signals across time and space.

The brain integrates information from multiple sensory modalities and, through this process, generates a coherent and apparently seamless percept of the external world. Although multisensory integration typically binds information that is derived from the same event, when multisensory cues are somewhat discordant they can result in illusory percepts such as the "ventriloquism effect." These biases in stimulus localization are generally accompanied by the perceptual unification of the two stimuli. In the current study, we sought to further elucidate the relationship between localization biases, perceptual unification and measures of a participant's uncertainty in target localization (i.e., variability). Participants performed an auditory localization task in which they were also asked to report on whether they perceived the auditory and visual stimuli to be perceptually unified. The auditory and visual stimuli were delivered at a variety of spatial (0 degrees, 5 degrees, 10 degrees, 15 degrees ) and temporal (200, 500, 800 ms) disparities. Localization bias and reports of perceptual unity occurred even with substantial spatial (i.e., 15 degrees ) and temporal (i.e., 800 ms) disparities. Trial-by-trial comparison of these measures revealed a striking correlation: regardless of their disparity, whenever the auditory and visual stimuli were perceived as unified, they were localized at or very near the light. In contrast, when the stimuli were perceived as not unified, auditory localization was often biased away from the visual stimulus. Furthermore, localization variability was significantly less when the stimuli were perceived as unified. Intriguingly, on non-unity trials such variability increased with decreasing disparity. Together, these results suggest strong and potentially mechanistic links between the multiple facets of multisensory integration that contribute to our perceptual Gestalt.

Acoustic Stimulation↗

PubMed2003

Visual localization ability influences cross-modal bias.

The ability of a visual signal to influence the localization of an auditory target (i.e., "cross-modal bias") was examined as a function of the spatial disparity between the two stimuli and their absolute locations in space. Three experimental issues were examined: (a) the effect of a spatially disparate visual stimulus on auditory localization judgments; (b) how the ability to localize visual, auditory, and spatially aligned multisensory (visual-auditory) targets is related to cross-modal bias, and (c) the relationship between the magnitude of cross-modal bias and the perception that the two stimuli are spatially "unified" (i.e., originate from the same location). Whereas variability in localization of auditory targets was large and fairly uniform for all tested locations, variability in localizing visual or spatially aligned multisensory targets was much smaller, and increased with increasing distance from the midline. This trend proved to be strongly correlated with biasing effectiveness, for although visual-auditory bias was unexpectedly large in all conditions tested, it decreased progressively (as localization variability increased) with increasing distance from the midline. Thus, central visual stimuli had a substantially greater biasing effect on auditory target localization than did more peripheral visual stimuli. It was also apparent that cross-modal bias decreased as the degree of visual-auditory disparity increased. Consequently, the greatest visual-auditory biases were obtained with small disparities at central locations. In all cases, the magnitude of these biases covaried with judgments of spatial unity. The results suggest that functional properties of the visual system play the predominant role in determining these visual-auditory interactions and that cross-modal biases can be substantially greater than previously noted.

Adult↗

PubMed2000

Hemispheric asymmetries and gender influence Rembrandt's portrait orientations.

For centuries painters have predominantly painted portraits with the model's left-cheek facing the viewer. This has been even more prevalent with females ( approximately 68%) than males ( approximately 56%). Numerous portraits painted by Rembrandt typify this unexplained phenomenon. In a preliminary experiment, subjects judged 24 emotional and social character traits in 20 portraits by Rembrandt. A factor analysis revealed that females with their left cheek exposed were judged to be much less socially appealing than less commonly painted right-cheeked females. Conversely, the more commonly painted right-cheeked males were judged to be more socially appealing than either left-cheeked males or females facing either direction. It is hypothesized that hemispheric asymmetries regulating emotional facial displays of approach and avoidance influenced the side of the face Rembrandt's models exposed due to prevailing social norms. A second experiment had different subjects judge a different collection of 20 portraits by Rembrandt and their mirror images. Mirror-reversed images produced the same pattern of results as their original orientation counterparts. Consequently, hemispheric asymmetries that specify the emotional expression on each side of the face are posited to account for the obtained results.

Brain↗

PubMed2000

T-junctions in inhomogeneous surrounds.

In an inhomogeneous checkerboard surround, the lighter check darkens an incremental test patch more than the darker check lightens it. However, decremental test patches are influenced equally [Schirillo & Shevell, 1996. Vision Research, 36, 1783-1796]. In the current study, we manipulate the spatial arrangement of a checkerboard surround to produce T-junctions that perceptually group the checks with the test patch. These stimuli alter the inducing effects of the checks. For one modified surround, increments appeared approximately 8% darker and decrements appeared approximately 10% lighter over the original checkerboard surround prior to modification. In a second modified surround, that resembled White's illusion [White, 1979. Perception, 8, 413-416], increments again appeared approximately 8% darker, while decrements appeared a dramatic approximately 23% lighter over the original checkerboard surround prior to modification. These enhanced induction effects are postulated to result from the addition of specific T-junctions. However, these grouping effects remain subservient to the asymmetrical induction effects found by Schirillo and Shevell (1996).

Adaptation, Ocular↗

PubMed2000

Role of perceptual organization in chromatic induction.

Color matches between two small patches were made in a display containing ten larger regions of different chromaticities. The spatial organization of the ten regions was varied while keeping constant the immediate surround of each patch as well as the space-average chromaticity of the entire stimulus. Different spatial arrangements were designed to alter the perceptual organization inferred by the observer without changing the ensemble of chromaticities actually in view. For example, one arrangement of the ten regions was consistent with five surfaces under two distinct illuminations, with one edge within the display (an "apparent illumination edge") dividing the stimulus into two areas, one under illuminant A and the other under illuminant C. Another spatial arrangement had the ten regions configured to induce an observer to infer ten surfaces under a single illumination. When the ten regions were arranged with an apparent illumination edge, the patch within the area of illuminant C was perceived as bluer than when the same patch and immediate surround were presented without an apparent illumination edge. The results are accounted for by positing that observers group together regions sharing the same inferred illumination, with a consequent effect on color perception: A fixed patch-within-surround shifts in hue and saturation toward the perceived illumination. We suggest that the change in color perception in a complex scene that results from a difference in real illumination may be caused by the inferred illumination at the perceptual level, not directly by the physical change in the light absorbed by photoreceptors.

Adult↗

PubMed1999

Surround articulation. I. Brightness judgments.

It has been hypothesized that brightness judgments require an estimate of the illuminant. Making this estimate is difficult since luminance edges can be the result of changes in either illumination or reflectance. Articulation is the addition of equally spaced incremental and decremental patches within a surround while preserving the surround's space-average luminance. It is proposed that articulation enhances the inference that the surround's luminance edge is due to a change in illumination rather than in reflectance. Articulation results in a corresponding shift in brightness judgments for test-patch increments but not for decrements. This finding concurs with Arend and Goldstein's [J. Opt. Soc. Am. A 4, 2281 (1987)] reported shifts in brightness as simple center-surround stimuli are transformed into more complex ecologically valid Mondrians.

Adult↗

PubMed1999

Surround articulation. II. Lightness judgments.

It has been hypothesized that to achieve color constancy, lightness judgments require an estimate of the illuminant. A companion paper [J. Opt. Soc. Am. A 16, 793 (1999)] suggests that surround articulation enhances the likelihood that a global luminance edge will be interpreted as being due to changes in illumination rather than in reflectance. Articulation is the process of adding equally spaced incremental and decremental patches within a surround while preserving the surround's space-average luminance. Such a process results in lightness judgments that correlate perfectly with equal local ratio matches. For decrements, lightness constancy does not require articulation. These findings help explain why Arend and Goldstein [J. Opt. Soc. Am. A 4, 2281 (1987)] obtained color constancy with complex Mondrian surrounds but not with simple center surrounds.

Adult↗

PubMed1997

An account of brightness in complex scenes based on inferred illumination.

Achromatic brightness matches between two small patches were measured in a display containing ten larger regions of different luminances. The spatial organization of the ten regions was varied while keeping constant the immediate surround (and thus local contrast) of each patch as well as the average luminance of the entire stimulus. Various spatial arrangements were designed to alter the illumination inferred by the observer without changing the ensemble of luminances actually in view. Some spatial arrangements of the ten regions were consistent with five (simulated) surfaces under two distinct levels of illumination, with one luminance edge within the display (an 'apparent illumination edge') dividing the stimuli into an area of lower illumination and an area of higher illumination. In other spatial arrangements the ten regions were configured so that no luminance edge in the display could be interpreted as an ecologically valid illumination edge that provides a parsimonious interpretation of the ten regions; these conditions were designed to induce observers to infer ten surfaces under a single illuminant. When the ten regions were arranged with an apparent illumination edge, the patch within the area of lower perceived illumination was perceived as dimmer than when the same patch and immediate surround were presented with no apparent illumination edge. The results are interpreted by positing that the apparent illumination edge causes an observer to group together regions under the same perceived illuminant, with a consequent effect on brightness: lowering or raising the level of a perceived illuminant causes a patch of fixed contrast to be perceived as less bright or more bright, respectively, just as occurs when lowering or raising the level of real illumination. It is suggested that changes in brightness in a complex scene that result from a change in real illumination may be caused by a difference in inferred illumination at the perceptual level, not by simply a change in the amount of light absorbed by photoreceptors.

Adult↗

PubMed1996

Brightness contrast from inhomogeneous surrounds.

The luminance of a test within an inhomogeneous ("checkerboard") surround was adjusted to match the brightness of a comparison patch within a uniform surround. All stimuli were achromatic. Both surrounds had the same space-averaged luminance. With an incremental comparison patch, a test-within-checkerboard at a luminance between the luminances of the brighter and dimmer checks appears dimmer than if viewed within the uniform surround. A decremental comparison patch, however, is matched by a test luminance that is little affected by the inhomogeneity of the surround. In general, the brightness of the test is mediated neither by the space-averaged luminance of an inhomogeneous surround, nor by any equivalent uniform surround, regardless of luminance. We consider alternative models for the brightness of a region that is neither strictly an increment nor decrement with respect to contiguous surrounding surfaces.

Adaptation, Ocular↗

PubMed1995

Field additivity of the middle-wavelength cone pathway under various test and field configurations.

The field additivity of the M-cone pathway was measured with psychometric functions at 10 times absolute threshold on monochromatic fields and their mixtures. Observers detected a 500 nm test on 530 or 610 nm fields, and a 530 nm test on 481 or 622 nm fields. For both sets of wavelengths, field additivity held with the 1 deg test, 10 deg field condition which defines II-4 and with the 3.6 min are test on a 8.6 min arc field used to isolate the M fundamental by Stockman [(1983) Ph. D. thesis, Trinity College, Cambridge University, Cambridge]. Sub-additivity occurred for a 1 deg test on a 1 deg field, a condition for Foster's "spectral sharpening" which may evince opponency.

Adult↗

PubMed1995

Illumination change at a depth edge can reduce lightness constancy.

Lightness constancy requires that a surface retain its lightness not only when the illumination is changed but also when the surface is moved from one background to another. Occlusion of one surface by another frequently results in a retinal juxtaposition of patches under different illuminations. At such edges, retinal luminance ratios can be much higher than in scenes with a single illumination. We demonstrate that such retinal adjacencies can produce failures of lightness constancy. We argue that they are responsible for departures from perfect lightness constancy in two prior experiments that examined the effects of depth relations on lightness constancy.

Adult↗

PubMed1993

Lightness and brightness judgments of coplanar retinally noncontiguous surfaces.

Several experiments reveal that judgments of lightness and brightness of an achromatic surface depend, in part, on the luminances of other surfaces perceived to share the same depth plane, even if the surfaces are well separated on the retina. Two Mondrians, simulated on a CRT, were viewed through a haploscope. The more highly illuminated Mondrian contained a comparison patch and appeared nearer than the more dimly illuminated Mondrian, which contained the test patch. By independently varying the disparity of the test patch, observers could make the test patch appear to be in the depth plane of either the dimly or the highly illuminated Mondrian. Observers set the luminance of the test patch to match that of the comparison patch. The test was set as high as 15% more luminous when it was perceived in the depth plane of the highly illuminated rather than the dimly illuminated Mondrian. Both brightness and lightness judgments were affected by the perceived depth of the test, although the lightness judgments of inexperienced observers sometimes were dominated by local-contrast matching.

Adult↗