Perceptual aftereffects of sustained convergence

Attention, Perception, & Psychophysics - Fixating a target for 6 or 8 min was shown to produce distance aftereffects that varied in direction (i.e., over- or underestimation) and magnitude as a...     

Perceptual asymmetries in audition

Visual feature extraction has been investigated using search experiments. Targets that contain a feature not present in the distractors are easier to detect than if they do not, leading to search asymmetries. If sounds are decomposed into features in the auditory system, there might be asymmetries in analogous tasks. Six experiments investigating this are described. Strong asymmetries were identified, with frequency-modulated targets easier to detect among pure-tone distractors than vice versa and longer sounds easier to select from short distractors than the reverse. It is demonstrated that this asymmetry is not a result of peripheral limitations. In contrast, no asymmetries were observed between high- and low-frequency tones or between short 3-tone sequences differing only in their temporal structure. The results are discussed with reference to models of perceptual grouping and attention, the applicability of analogies between vision and audition, and possible physiological correlates. The paradigm provides a new way in which to investigate auditory feature extraction.     

Perceptual adaptation to facial asymmetries

Humans and other animals are highly sensitive to deviations from bilateral symmetry and prefer symmetric mates. Fluctuating asymmetries (FAs) are random deviations from perfect symmetry that can result from developmental instability. Human perceptions of facial asymmetry are driven by FAs and insensitive to directional asymmetries (DAs), which have a consistent direction of bias (e.g., left side always larger) across the population and are unrelated to developmental stability. We hypothesized that perceptual adaptation may filter out DAs and provide a proximate mechanism for this perceptual focus on FAs. We created a small population of faces with DAs by applying a unilateral distortion to the same side of each face. After 5 min of adaptation, (new) faces with these DAs looked less asymmetric and the most symmetric-looking distortion shifted toward the adapting asymmetry level. Parallel changes occurred for attractiveness. We suggest that perceptual adaptation may provide the proximate mechanism for an evolutionarily adaptive focus on FAs.     

Perceptual asymmetries in face recognition

Four experiments were carried out to investigate perceptual asymmetries in face recognition. Perceptual asymmetries favoring the half-face on the observer's left were found under free viewing conditions for both unfamiliar faces (Experiment 1) and famous faces (Experiment 3). For unfamiliar faces, this asymmetry was not obtained when fixation was controlled by presenting faces tachistoscopically (Experiment 2). For famous faces, the perceptual asymmetry favoring the half-face normally seen on the left did not appear to be retained in memory (Experiments 3 and 4). Asymmetries in face perception have been explained in terms of a direct access model of laterally effects. However, these results raise the possibility that asymmetric scanning or attentional factors may be important.     

Perceptual aftereffects of sustained fixation and oculomotor changes

Several conditions induce correlated perceptual and oculomotor changes. Often the perceptual aftereffects are treated as a result of the oculomotor ones. Some results are reported that cast doubt on this interpretation of the aftereffects of sustained convergence. First, the inspection distance that induces no aftereffect is nearer than the vergence resting position. Second, there are at least two situations in which the expected correlation between perceptual and oculomotor changes breaks down: (1) inspection of a near stimulus below eye level tends to induce a subsequent overestimation of the distance of a test stimulus that is accompanied by an exophoric shift instead of the expected exophoric one, and (2) closing one's eyes for some minutes induces an exophoric shift without a perceptual aftereffect. These results suggest that at least in some situations perceptual and oculomotor changes may be functionally independent.     

Response scatter in measuring changing-loudness aftereffects: evidence for simplified processing of auditory motion-in-depth and potential collision

Researchers have postulated 2 mechanisms for processing auditory motion: a direct mechanism processing motion itself and an indirect mechanism sensitive to location over discrete points in time. Measuring aftereffects of azimuthal motion by nulling entails scattered responding, which is attributed to a conflict between direct and indirect mechanisms. In this experiment, the author obtained nulls following adaptation to changing sound level, a property of approaching or receding sound sources, and for nonadaptation. Test stimuli ranged in duration from 1.0 to 2.5 s. Longer test stimuli evinced reductions in both changing-loudness aftereffects and the associated response scatters. However, the latter matched the nonadaptation response scatters. The author suggests that judging longer test stimuli is easier, so an indirect mechanism need not be invoked. Simplified processing of changing sound level may underlie the rapid responses required for potential collision.     

Perceptual asymmetries are preserved in short-term memory tasks

Visual performance is heterogeneous at isoeccentric locations; it is better on the horizontal than on the vertical meridian and worse at the upper than at the lower region of the vertical meridian (Carrasco, Talgar, & Cameron, 2001; Talgar & Carrasco, 2002). It is unknown whether these performance inhomogeneities are also present in spatial frequency tasks and whether asymmetries present during encoding of visual information also emerge in visual short-term memory (VSTM) tasks. Here, we investigated the similarity of the perceptual and VSTM tasks in spatial frequency discrimination (Experiments 1 and 2) and perceived spatial frequency (Experiments 3 and 4). We found that (1) performance in both simultaneous (perceptual) and delayed (VSTM) spatial frequency discrimination tasks varies as a function of location; it is better along the horizontal than along the vertical meridian; and (2) perceived spatial frequency in both tasks is higher along the horizontal than along the vertical meridian. These results suggest that perceived spatial frequency may mediate performance differences in VSTM tasks across the visual field, implying that the quality with which we encode information affects VSTM.     

Perceptual asymmetries in normal children and children with attention deficit/hyperactivity disorder

Perceptual asymmetries in normal right-handed children (7-12 years of age) and children with attention deficit/hyperactivity disorder (ADHD), combined type, were investigated using various chimeric stimuli in free-viewing conditions. In the face-matching task, participants indicated which of two symmetrical face chimeras more closely resembled the original; in the chimeric faces task, participants indicated which of a pair of faces appeared happier; and in the grey scales task participants indicated which of two shaded rectangles appeared to be darker overall. Leftward biases were found for normal children with no effects of age. Contrary to expectations, normal leftward biases were also found for ADHD children in the face-matching and the chimeric faces tasks; however, a significant leftward bias was not observed in the grey scales task. The absence of anomalous perceptual bias in ADHD children on these purely perceptual tasks, suggests that anomalous perceptual asymmetries observed in other tasks (line bisection and cancellation tasks) may have been confounded by the motor response, and/or the explicit spatial components of those tasks.     

Perceptual grouping, not emotion, accounts for search asymmetries with schematic faces

Several different explanations have been proposed to account for the search asymmetry (SA) for angry schematic faces (i.e., the fact that an angry face target among friendly faces can be found faster than vice versa). The present study critically tested the perceptual grouping account, (a) that the SA is not due to emotional factors, but to perceptual differences that render angry faces more salient than friendly faces, and (b) that the SA is mainly attributable to differences in distractor grouping, with angry faces being more difficult to group than friendly faces. In visual search for angry and friendly faces, the number of distractors visible during each fixation was systematically manipulated using the gaze-contingent window technique. The results showed that the SA emerged only when multiple distractors were visible during a fixation, supporting the grouping account. To distinguish between emotional and perceptual factors in the SA, we altered the perceptual properties of the faces (dented-chin face) so that the friendly face became more salient. In line with the perceptual account, the SA was reversed for these faces, showing faster search for a friendly face target. These results indicate that the SA reflects feature-level perceptual grouping, not emotional valence.     

Perceptual orientational asymmetries: A comparison of visual and haptic space

Stimulus orientation discrimination was investigated in visual and haptic modalities under conditions of simultaneous matching and memory. Discrimination of vertical and horizontal was significantly more accurate than discrimination of oblique stimulus orientations (45°, 135°, 225°, and 315°) for both modalities; haptic errors, however, were significantly greater at each orientation. While subjects were reliably more accurate in visually matching oblique stimulus orientations to a standard than producing them from memory, for the haptic modality, differences between memory and matching conditions were less consistent across the orientations sampled.     

Perceptual asymmetries in left- and right-handers for cartoon and real faces

We examined 40 left-handers and 40 right-handers on two free-vision tests of face processing. A chimeric face composed of a smiling half-face joined to either a neutral half-face (real faces) or a sad half-face (cartoon faces) and its mirror image were presented on each trial. Subjects judged which chimeric face looked happier, the one with the smile to the left or the one with the smile to the right. Right-handers, but not left-handers, had a highly significant leftward attentional bias, since chimeras with the smile to the left were judged happier than those with the smile to the right. The cartoon- and real-face tasks did not differ in the mean perceptual asymmetries they elicited. However, correlations between attentional-asymmetry scores for the two tasks, although high for both left- and right-handers, were significantly smaller than task reliabilities. Thus, the cartoon- and real-face tasks overlap to a major extent in the lateralized processes they measure, but to a lesser extent, they also index different lateralized processes.     

Perceptual asymmetries reflect developmental changes in the neuropsychological mechanisms of emotion recognition

To study how perceptual asymmetries in the recognition of emotion reflect developmental changes in processing affective information, a fused rhyming dichotic word test with positive, negative, and neutral stimuli was administered to adults and children. Results suggested that the hemisphere in which affective information is initially processed affects the strength of perceptual asymmetry and that children's perceptual processing of emotional information is constrained by limited computational resources. Another experiment ruled out effects of volitional shifting of attention to emotional stimuli. These data further confirm that emotional processing involves integration of neural systems across brain regions, including distributed systems that support arousal and recognition. General developmental factors, such as processing capacity, contribute to the coordination of multiple systems responsible for processing emotional information.     

Perceptual asymmetries for free viewing of several types of chimeric stimuli.

We examined perceptual biases of right-handers on six free-vision chimeric tasks; two involving a judgement of happiness of a facial expression in photographic and cartoon chimeras, two involving a judgement of femininity in male/female photographic and cartoon chimeras, and two involving a spatial judgement of nonface chimeric stimuli. All four of the face tasks and one of the nonface tasks elicited left spatial field biases of varying magnitudes, and perceptual asymmetries on all tasks were positively correlated. However, multiple correlational analyses revealed that these tests shared differing proportions of variance with each other. Results indicate that, in addition to a common factor or set of factors contributing to lateral biases that is independent of both the nature of the stimulus and whether the stimulus engages lateralized mechanisms, there are distinct lateralized mechanisms which yield different patterns of perceptual asymmetries for different stimuli.     

Perceptual asymmetries are preserved in memory for highly familiar faces of self and friend

We investigated the effect of familiarity on people's perception of facial likeness by asking participants to choose which of two mirror-symmetric chimeric images (made from the left or right half of a photograph of a face) looked more like an original image. In separate trials the participants made this judgment for their own face and for the face of a close friend; half of them matched to a true image of the original and half matched to a mirror image of the original. In the case of matching to a friend's face presented in the familiar orientation, over 80% of participants chose the left-left composite to be a better likeness to the original, whereas only 62% showed the same left-side bias when matching to a mirror image. The difference is significant, and the result contrasts markedly with a second experiment where participants who were unfamiliar with the faces showed comparable left-side biases when matching to true or mirror reversed images. The result suggests that perceptual asymmetries are retained in our long-term memory for highly familiar faces. While matching to images of self also showed an effect of familiarity, the data in this condition show less evidence of perceptual asymmetry and are discussed in relation to recent research on the representation of one's own face.     

Motion aftereffects with rotating ellipses

Summary The perceptual outcome and the motion-aftereffect duration generated by the rotation on the frontal plane of an ellipse with a bar depend on whether the bar is placed along the major or the minor axis. When the bar is placed along the minor axis, a stereokinetic transformation occurs, and the pattern looks like a tilting ring with a perpendicular bar moving rigidly with it. Placing the bar along the major axis prevents the stereokinetic transformation: subjects report deformations and relative motion of the bar with respect to the ellipse. We found that motion aftereffects last longer when the bar is placed along the minor rather than along the major axis. A series of experiments was carried out to investigate whether differences in aftereffect duration are related to the stereokinetic transformation. Results seem to suggest that they are not.The authors' names are in alphabetical order.     

Colored aftereffects produced with moving edges

Colored aftereffects that lasted as long as 6 weeks were produced with moving patterns of parallel black and white stripes or with black and white spirals. During adaptation, the patterns moved periodically in opposite directions, each direction paired with one illuminant, red or green. When the moving patterns were later viewed in white light, S saw the red and green colors, but they were related in the opposite way to the direction of motion. The red and green aftereffects were also produced by other pairs of illuminants, red and white, white and green, reddish-yellow and white, and white and greenish-yellow. The aftereffects did not occur unless, during adaptation, the stripes moved in both directions, each direction paired with a different color. The aftereffect was elicited by stripe motion over the retina—it was seen when the eye swept over a pattern of stationary stripes. The aftereffect desaturated when the retinal orientation of the stripes was changed from the adaptation orientation. Saturation was increased by longer exposure and slower speed during adaptation and by faster speed and a more rapid rate of altemation during the test. The luminance of the adaptation light seemed to have little effect. The aftereffect did not transfer from one eye to the other, and it did not change retinal locus, as was shown when clear images of a colored square that lasted several days were produced with a spiral. S ftxated the spiral’s center. The spiral rotated altemately in opposite directions. A red square with a green surround was projected on the center of the spiral when it rotated in one direction; a green square with a red surround was used when it rotated in the other direction. Following 50 min of adaptation, colored images of the squares were seen when the center of the spiral was ftxated and the direction of     

Color-selective tilt aftereffects with subjective contours

Displays yielding edges visible at sites where the visual stimulus was homogeneous (subjective contours) as well as with edges defined by spatial discontinuities in luminance (real contours) were used to induce the tilt aftereffect. Under monoptic conditions, the aftereffect was larger when the inspection and test edges were shown in the same colored light than when they were shown in different colored lights. Under dichoptic conditions (display of inspection edges to one eye and test edges to the other eye), the aftereffect was reduced in size and it was no longer selective to the color relationship between the inspection and test stimuli. Similar results were obtained with subjective and real contours. In the recent literature, subjective contours have been treated as products of cognitive and inferential operations, whereas neural edge detectors have been implicated in the perception of real contours. The present data suggest, however, the need for caution in attributing the perception of real and subjective contours to fundamentally different processes.     

Orientation-specific luminance aftereffects

Prolonged viewing of bright vertical (horizontal) gratings alternating with dim horizontal (vertical) gratings generates negative brightness aftereffects that are contingent on the orientation of orthogonal test gratings. The effect is measured by a brightness cancellation technique, similar to the color cancellation technique used in measuring McCollough effects. Like the latter, brightness aftereffects appear to persist for long periods. The magnitude of these aftereffects is a positive monotonic function of the luminance difference between the inducing gratings, and it depends on the conditions of induction; monocular induction generates larger aftereffects than binocular induction does. The aftereffect transfers interocularly, although its magnitude in the contralateral eye is substantially attenuated; binocular measurement, following monocular induction, results in even smaller aftereffects. An attempt to understand these findings within the computational model of brightness perception developed by Grossberg and Mingolla (1985a, 1985b) is presented.     

Curvature-specific color aftereffects

Adaptation to convex and concave arcs in different colored light results in curvature-specific color aftereffects when arcs are later viewed in white light. In three experiments, it was shown that these color aftereffects often are partial (restricted to limited regions of the test arcs) rather than uniform, and in addition that aftereffects induced by exposure to arcs transfer to straight-line displays of particular orientation, and vice versa. These data were interpreted as evidence that arcs are processed in the visual system in relation to the orientations of local straight line approximations instead of on a global basis. In these terms, curvature-specific color aftereffects are merely complex forms of the orientation-specific color aftereffects first described by McCollough (1965).