Form and Function in Information for Visual Perception.

Visual perception involves spatially and temporally coordinated variations in diverse physical systems: environmental surfaces and symbols, optical images, electro-chemical activity in neural networks, muscles, and bodily movements-each with a distinctly different material structure and energy. The fundamental problem in the theory of perception is to characterize the information that enables both perceptual awareness and real-time dynamic coordination of these diverse physical systems. Gibson's psychophysical and ecological conception of this problem differed from that of mainstream science both then and now. The present article aims to incorporate Gibson's ideas within a general conception of information for visual perception. We emphasize the essential role of spatiotemporal form, in contrast with symbolic information. We consider contemporary understanding of surface structure, optical images, and optic flow. Finally, we consider recent evidence about capacity limitations on the rate of visual perception and implications for the ecology of vision.

Correction to: A Limiting Channel Capacity of Visual Perception: Spreading Attention Divides the Rates of Perceptual Processes.

An error occurred in labeling the data in Fig. 5a-b, p. 2661. The figure caption is correct as printed. A corrected Fig. 5 is below.

A Limiting Channel Capacity of Visual Perception: Spreading Attention Divides the Rates of Perceptual Processes.

This study investigated effects of divided attention on the temporal processes of perception. During continuous watch periods, observers responded to sudden changes in the color or direction of any one of a set of moving objects. The set size of moving objects was a primary variable. A simple detection task required responses to any display change, and a selective task required responses to a subset of the changes. Detection rates at successive points in time were measured by response time (RT) hazard functions.The principal finding was that increasing the set size divided the detection rates-and these divisive effects were essentially constant over time and over the time-varying influence of the target signals and response tasks. The set size, visual target signal, and response task exerted mutually invariant influence on detection rates at given times, indicating independent joint contributions of parallel component processes. The lawful structure of these effects was measured by RT hazard functions but not by RTs as such. The results generalized the time-invariant divisive effects of set size on visual process rates found by Lappin, Morse, & Seiffert (Attention, Perception, & Psychophysics, 78, 2469-2493, 2016). These findings suggest that the rate of visual perception has a limiting channel capacity.

Temporal Limits of Visual Motion Processing: Psychophysics and Neurophysiology.

Under optimal conditions, just 3-6 ms of visual stimulation suffices for humans to see motion. Motion perception on this timescale implies that the visual system under these conditions reliably encodes, transmits, and processes neural signals with near-millisecond precision. Motivated by in vitro evidence for high temporal precision of motion signals in the primate retina, we investigated how neuronal and perceptual limits of motion encoding relate. Specifically, we examined the correspondence between the time scale at which cat retinal ganglion cells in vivo represent motion information and temporal thresholds for human motion discrimination. The timescale for motion encoding by ganglion cells ranged from 4.6 to 91 ms, and depended non-linearly on temporal frequency, but not on contrast. Human psychophysics revealed that minimal stimulus durations required for perceiving motion direction were similarly brief, 5.6-65 ms, and similarly depended on temporal frequency but, above ~10%, not on contrast. Notably, physiological and psychophysical measurements corresponded closely throughout (r = 0.99), despite more than a 20-fold variation in both human thresholds and optimal timescales for motion encoding in the retina. The match in absolute values of the neurophysiological and psychophysical data may be taken to indicate that from the lateral geniculate nucleus (LGN) through to the level of perception little temporal precision is lost. However, we also show that integrating responses from multiple neurons can improve temporal resolution, and this potential trade-off between spatial and temporal resolution would allow for loss of temporal resolution after the LGN. While the extent of neuronal integration cannot be determined from either our human psychophysical or neurophysiological experiments and its contribution to the measured temporal resolution is unknown, our results demonstrate a striking similarity in stimulus dependence between the temporal fidelity established in the retina and the temporal limits of human motion discrimination.

Spatial suppression promotes rapid figure-ground segmentation of moving objects.

Segregation of objects from their backgrounds is a fundamental visual function and one that is particularly effective when objects are in motion. Theoretically, suppressive center-surround mechanisms are well suited for accomplishing motion segregation. This longstanding hypothesis, however, has received limited empirical support. We report converging correlational and causal evidence that spatial suppression of background motion signals is critical for rapid segmentation of moving objects. Motion segregation ability is strongly predicted by both individual and stimulus-driven variations in spatial suppression strength. Moreover, aging-related superiority in perceiving background motion is associated with profound impairments in motion segregation. This segregation deficit is alleviated via perceptual learning, but only when motion segregation training also causes decreased sensitivity to background motion. We argue that perceptual insensitivity to large moving stimuli effectively implements background subtraction, which, in turn, enhances the visibility of moving objects and accounts for the observed link between spatial suppression and motion segregation.

Charles "Erik" Eriksen (1923-2018).

A towering figure in experimental psychology, Charles W. Eriksen, passed away in February this year. "Erik" made extensive original and lasting contributions to both research methods and theories in several areas of psychology, especially involving visual information processing. His research exhibited consistent concerns with experimental methods for distinguishing among alternative explanations and distinguishing perception from behavior. Erik pioneered many research methods now in common use-including converging operations, visual search, rapid serial presentations, the stop-signal paradigm, temporal integration in form perception, spatial cues for guiding selective attention, and the flankers task. He also introduced and tested many theories of selective attention. Erik was the founding editor of Perception & Psychophysics, and served for 23 years as its principal editor. An impressive and unforgettable person, Erik was a compelling personification of "the greatest generation."

Perceptual training yields rapid improvements in visually impaired youth.

Visual function demands coordinated responses to information over a wide field of view, involving both central and peripheral vision. Visually impaired individuals often seem to underutilize peripheral vision, even in absence of obvious peripheral deficits. Motivated by perceptual training studies with typically sighted adults, we examined the effectiveness of perceptual training in improving peripheral perception of visually impaired youth. Here, we evaluated the effectiveness of three training regimens: (1) an action video game, (2) a psychophysical task that combined attentional tracking with a spatially and temporally unpredictable motion discrimination task, and (3) a control video game. Training with both the action video game and modified attentional tracking yielded improvements in visual performance. Training effects were generally larger in the far periphery and appear to be stable 12 months after training. These results indicate that peripheral perception might be under-utilized by visually impaired youth and that this underutilization can be improved with only ~8 hours of perceptual training. Moreover, the similarity of improvements following attentional tracking and action video-game training suggest that well-documented effects of action video-game training might be due to the sustained deployment of attention to multiple dynamic targets while concurrently requiring rapid attending and perception of unpredictable events.

The channel capacity of visual awareness divided among multiple moving objects.

If attention is distributed among multiple moving objects, how does this divided attention affect the temporal process for detecting a specific target motion? Well-trained observers in three experiments monitored ongoing random motions of multiple objects, trying to rapidly detect non-random target motions. Response time hazard rates revealed a simple lawful structure of the detection processes. Target detection rates (hazard rates, in bits /s) were inversely proportional to the number of observed objects. Detection rates at any response time and in any condition equaled a product of two parallel (functionally independent and concurrent) visual processes: visual awareness and motion integration. The rate of visual awareness was inversely proportional to Set Size (n = 1-12), constant over time, and invariant with integrated motion information. Thus, a single rate parameter, indicating a constant channel capacity of visual awareness, described detection rates over a wide range of conditions and response times. During an initial interval of roughly 0.5 s, detection rates increased proportionally with the duration and length of motion; but after this initial integration, detection rates were constant, independent of the time the target remained undetected. The relationship between the quantity of visual information and detection rates was simpler than anticipated by contemporary theories of attention, perception, and performance.

What is binocular disparity?

What are the geometric primitives of binocular disparity? The Venetian blind effect and other converging lines of evidence indicate that stereoscopic depth perception derives from disparities of higher-order structure in images of surfaces. Image structure entails spatial variations of intensity, texture, and motion, jointly structured by observed surfaces. The spatial structure of binocular disparity corresponds to the spatial structure of surfaces. Independent spatial coordinates are not necessary for stereoscopic vision. Stereopsis is highly sensitive to structural disparities associated with local surface shape. Disparate positions on retinal anatomy are neither necessary nor sufficient for stereopsis.

Peripheral vision of youths with low vision: motion perception, crowding, and visual search.

PURPOSE: Effects of low vision on peripheral visual function are poorly understood, especially in children whose visual skills are still developing. The aim of this study was to measure both central and peripheral visual functions in youths with typical and low vision. Of specific interest was the extent to which measures of foveal function predict performance of peripheral tasks. METHODS: We assessed central and peripheral visual functions in youths with typical vision (n = 7, ages 10-17) and low vision (n = 24, ages 9-18). Experimental measures used both static and moving stimuli and included visual crowding, visual search, motion acuity, motion direction discrimination, and multitarget motion comparison. RESULTS: In most tasks, visual function was impaired in youths with low vision. Substantial differences, however, were found both between participant groups and, importantly, across different tasks within participant groups. Foveal visual acuity was a modest predictor of peripheral form vision and motion sensitivity in either the central or peripheral field. Despite exhibiting normal motion discriminations in fovea, motion sensitivity of youths with low vision deteriorated in the periphery. This contrasted with typically sighted participants, who showed improved motion sensitivity with increasing eccentricity. Visual search was greatly impaired in youths with low vision. CONCLUSIONS: Our results reveal a complex pattern of visual deficits in peripheral vision and indicate a significant role of attentional mechanisms in observed impairments. These deficits were not adequately captured by measures of foveal function, arguing for the importance of independently assessing peripheral visual function.

Fechner, information, and shape perception.

How do retinal images lead to perceived environmental objects? Vision involves a series of spatial and material transformations--from environmental objects to retinal images, to neurophysiological patterns, and finally to perceptual experience and action. A rationale for understanding functional relations among these physically different systems occurred to Gustav Fechner: Differences in sensation correspond to differences in physical stimulation. The concept of information is similar: Relationships in one system may correspond to, and thus represent, those in another. Criteria for identifying and evaluating information include (a) resolution, or the precision of correspondence; (b) uncertainty about which input (output) produced a given output (input); and (c) invariance, or the preservation of correspondence under transformations of input and output. We apply this framework to psychophysical evidence to identify visual information for perceiving surfaces. The elementary spatial structure shared by objects and images is the second-order differential structure of local surface shape. Experiments have shown that human vision is directly sensitive to this higher-order spatial information from interimage disparities (stereopsis and motion parallax), boundary contours, texture, shading, and combined variables. Psychophysical evidence contradicts other common ideas about retinal information for spatial vision and object perception.

High temporal precision for perceiving event offsets.

Characterizing the temporal limits of the human visual system has long been a central goal of vision research. Spanning three centuries of research, temporal order judgments have been used to estimate the temporal precision of visual processing, with nearly all the research focusing on onset asynchrony discriminations. Recent neurophysiological work, however, demonstrated that neural latencies for stimulus offsets are shorter and less variable than those following event onsets, suggesting that event offsets might provide more reliable timing cues to the visual system than event onsets. Here, we tested this hypothesis by measuring psychophysical thresholds for discriminating onset and offset asynchronies for both stationary and moving stimuli. In three experiments, we showed that offset asynchrony thresholds were indeed consistently lower and were less affected by stimulus variations than onset asynchrony thresholds. These findings are consistent with neurophysiology and suggest a possible role of offset signals as reliable timing references for visual events.

Spatial and temporal limits of motion perception across variations in speed, eccentricity, and low vision.

We evaluated spatial displacement and temporal duration thresholds for discriminating the motion direction of gratings for a broad range of speeds (0.06 degrees/s to 30 degrees/s) in fovea and at +/-30 degrees eccentricity. In general, increased speed yielded lower duration thresholds but higher displacement thresholds. In most conditions, these effects of speed were comparable in fovea and periphery, yielding relatively similar thresholds not correlated with decreased peripheral acuity. The noteworthy exceptions were interactive effects at slow speeds: (1) Displacement thresholds for peripheral motion were affected by acuity limits for speeds below 0.5 degrees/s. (2) Low-vision observers with congenital nystagmus had elevated thresholds for peripheral motion and slow foveal motion but resembled typically sighted observers for foveal motions at speeds above 1 degree/s. (3) Suppressive center-surround interactions were absent below 0.5 degrees/s and their strength increased with speed. Overall, these results indicate qualitatively different sensitivities to slow and fast motions. Thresholds for very slow motion are limited by spatial resolution, while thresholds for fast motion are probably limited by temporal resolution.

Recognition speed using a bioptic telescope.

PURPOSE: This study sought to quantify the training and the asymptotic efficiency of novice users of spectacle-mounted bioptic telescopes. METHODS: Fifteen subjects with simulated 20/200 central acuity were fitted with bioptic telescopes. We measured the speed with which subjects were able to use a bioptic telescope to locate and identify a small letter, which was presented peripherally in a crowded array of letters at +/-45 degrees eccentricity. Both the target onset and its location were random. Subjects participated in four experimental sessions for a total of 500 (short session group) or 1000 trials (long session group). RESULTS: After training, the letter recognition speed with a bioptic telescope decreased by about 800 ms. Most of the improvement, however, occurred within the first approximately 150 trials. There were no systematic differences between groups. The asymptotic recognition speed with a bioptic telescope was about 1000 ms, 450 ms longer than the recognition speed in the same task but with 20/20 vision. Preliminary measurements suggest that these learning effects persist over a period of several years. CONCLUSIONS: Evidently, novice users can quickly acquire proficiency in using a spectacle-mounted bioptic telescope. This task could be used to train new bioptic telescope users in a safe environment and to evaluate their progress.

Contextual modulations of center-surround interactions in motion revealed with the motion aftereffect.

Segregation of objects from their backgrounds is one of vision's most important tasks and one that is accomplished with ease. It is often hypothesized that suppressive center-surround receptive field interactions represent a key neural substrate underlying efficient figure-ground segregation, yet this intuitively appealing hypothesis has received very little experimental support. Using the motion aftereffect as an experimental tool, we explored this hypothesis by examining how surround suppression was affected by contextual manipulations that altered the perceived figure-ground relations but kept local motion signals unchanged. The results demonstrated that surround suppression was strong when the visual context implied a large moving field. On the other hand, when the contextual interpretation was consistent with a smaller moving object, surround suppression was greatly reduced. These findings are consistent with the notion that center-surround interactions play a role in segregating moving objects from backgrounds.

Weakened center-surround interactions in visual motion processing in schizophrenia.

Schizophrenia is often accompanied by a range of visual perception deficits, with many involving impairments in motion perception. The presence of perceptual abnormalities may impair neural processes that depend on normal visual analysis, which in turn may affect overall functioning in dynamic visual environments. Here, we examine the integrity of suppressive center-surround mechanisms in motion perception of schizophrenic patients. Center-surround suppression has been implicated in a range of visual functions, including figure-ground segregation and pursuit eye movements, visual functions that are impaired in schizophrenia. In control subjects, evidence of center-surround suppression is found in a reduced ability to perceive motion of a high-contrast stimulus as its size increases. This counterintuitive finding is likely a perceptual correlate of center-surround mechanisms in cortical area MT. We now show that schizophrenic patients exhibit abnormally weak center-surround suppression in motion, an abnormality that is most pronounced in patients with severe negative symptoms. Interestingly, patients with the weakest surround suppression outperformed control subjects in motion discriminations of large high-contrast stimuli. This enhanced motion perception of large high-contrast stimuli is consistent with an MT abnormality in schizophrenia and has a potential to disrupt smooth pursuit eye movements and other visual functions that depend on unimpaired center-surround interactions in motion.

Environmental context influences visually perceived distance.

What properties determine visually perceived space? We discovered that the perceived relative distances of familiar objects in natural settings depended in unexpected ways onthe surrounding visual field. Observers bisected egocentric distances in a lobby, in a hallway, and on an open lawn. Three key findings were the following: (1) Perceived midpoints were too far from the observer, which is the opposite of the common foreshortening effect. (2) This antiforeshortening constant error depended on the environmental setting--greatest in the lobby and hall but nonsignificant on the lawn. (3) Context also affected distance discrimination; variability was greater in the hall than in the lobby or on the lawn. A second experiment replicated these findings, using a method of constant stimuli. Evidently, both the accuracy and the precision of perceived distance depend on subtle properties of the surrounding environment.

Fine temporal properties of center-surround interactions in motion revealed by reverse correlation.

Center-surround interactions are a key property of visual motion mechanisms. Using a temporal reverse correlation method with human observers, we investigated perceptual interactions between a brief center motion (approximately 20 ms) and a surround that moved up-down with a new direction chosen randomly every 5 ms. The aim was to reveal interactions between center and surround motions and their dependency on relative direction, contrast, and timing. Hypothesizing that surround computation involves different neural circuitry than the center response, we manipulated surround contrast to affect the relative timing of center and surround signals. The reverse correlation analysis yielded temporal profiles of surround influence indicating, in 5 ms steps, the time course of the effect of the surround on the discriminability of center motion. The resulting temporal profiles varied systematically with contrast: as surround contrast decreased, both the latency and duration of its influence increased. This finding, consistent with longer and variable neural response latencies at low contrast, psychophysically reveals fine-scale temporal interactions between center and surround signals. Additionally, the strength of surround influence was correlated with psychophysical thresholds for discriminating center motion. The directionality of this relationship, however, depended only on center contrast. When center motion was high contrast, poor direction discrimination was associated with an increased probability of same-direction surround motions. Low-contrast center motion, however, was more discriminable when surrounded by motion in the same direction, regardless of surround contrast. This suggests that the previously reported adaptive nature of center-surround interactions in motion is driven primarily by the visibility of the center motion signals.