Theoretical and methodological approaches to apparent movement of short-range process and pattern perception

A variable raster and vector display processor interfaced with a PDP-11/23 computer is briefly described. Several experiments using random-dot cinematograms (RDCs) (raster display) and line segments (vector display) are discussed. The experiments on cooperative processes of apparent movement of RDCs and spatial-frequency-filtered RDCs showed that the average cooperative neighborhood of neural interaction is about 15 min arc of visual angle. In pattern perception, based on Julesz’s texton theory (1981) and Shaw’s attention model (1980), this study showed that the aperture of attention in serial and parallel processing is a function of feature gradient, set size, and eccentricity.     

Limited translation invariance of human visual pattern recognition

Visual object recognition is considered to be largely translation invariant. An earlier study (Foster & Kahn, 1985), however, has indicated that recognition of complex novel stimuli is partially specific to location in the visual field: It is significantly easier to determine the identity of two briefly displayed random patterns if both stimuli are presented at the same, rather than at different, locations. In a series ofsame/different discrimination tasks, we characterize the processes underlying this “displacement effect”: Horizontal and vertical translations are equally effective in reducing performance. Making the task more difficult by increasing pattern similarity leads to even higher positional specificity. The displacement effect disappears after rotation or contrast reversal of the patterns, indicating that positional specificity depends on relatively low levels of processing. Control experiments rule out explanations that are independent of visual pattern memory, such as spatial attention, eye movements, or retinal afterimages. Positional specificity of recognition is found only forsame trials. Our results demonstrate that position invariance, a widely acknowledged property of the human visual system, is limited to specific experimental conditions. Normalization models involving mental shifts of an early visual representation or of a window of attention cannot easily account for these findings.     

Abstract stimuli associated with threat through conditioning cannot be detected preattentively

Studies of anxiety suggest that threat stimuli can be identified preattentively, but this conclusion is questionable because of possible low-level perceptual confounds. Two experiments used visual search tasks in which abstract shapes were conditioned to carry neutral or negative valence. Experiment 1 found generally faster responses to threat-associated abstract stimuli but no evidence that they were detected preattentively, irrespective of trait anxiety level. A similar pattern was found in Experiment 2, in which individuals high in snake or spider fear showed no evidence of preattentive detection of abstract stimuli associated with their feared object. In contrast, implicit behavioral measures showed significant effects of conditioning, demonstrating that targets associated with threat were negatively evaluated in these experiments.     

Attentional effects on preattentive vision: spatial precues affect the detection of simple features

Most accounts of visual perception hold that the detection of primitive features occurs preattentively, in parallel across the visual field. Evidence that preattentive vision operates without attentional limitations comes from visual search tasks in which the detection of the presence of absence of a primitive feature is independent of the number of stimuli in a display. If the detection of primitive features occurs preattentively, in parallel and without capacity limitations, then it should not matter where attention is located in the visual field. The present study shows that even though the detection of a red element in an array of gray elements occurred in parallel without capacity limitations, the allocation of attention did have a large effect on search performance. If attention was directed to a particular region of the display and the target feature was presented elsewhere, response latencies increased. Results indicate that the classic view of preattentive vision requires revision.     

Pyramid algorithms for perceptual organization

Multiresolution (orpyramid) approaches to computer vision provide the capability of rapidly detecting and extracting global structures (features, regions, patterns, etc.) from an image. The human visual system also is able to spontaneously (orpreattentively) perceive various types of global structure in visual input; this process is sometimes calledperceptual organization. This paper describes a set of pyramid-based algorithms that can detect and extract these types of structure; included are algorithms for inferring three-dimensional information from images and for processing time sequences of images. If implemented in parallel on cellular pyramid hardware, these algorithms require processing times on the order of the logarithm of the image diameter.     

Where perception meets memory: A review of repetition priming in visual search tasks

What we have recently seen and attended to strongly influences how we subsequently allocate visual attention. A clear example is how repeated presentation of an object’s features or location in visual search tasks facilitates subsequent detection or identification of that item, a phenomenon known as priming. Here, we review a large body of results from priming studies that suggest that a short-term implicit memory system guides our attention to recently viewed items. The nature of this memory system and the processing level at which visual priming occurs are still debated. Priming might be due to activity modulations of low-level areas coding simple stimulus characteristics or to higher level episodic memory representations of whole objects or visual scenes. Indeed, recent evidence indicates that only minor changes to the stimuli used in priming studies may alter the processing level at which priming occurs. We also review recent behavioral, neuropsychological, and neurophysiological evidence that indicates that the priming patterns are reflected in activity modulations at multiple sites along the visual pathways. We furthermore suggest that studies of priming in visual search may potentially shed important light on the nature of cortical visual representations. Our conclusion is that priming occurs at many different levels of the perceptual hierarchy, reflecting activity modulations ranging from lower to higher levels, depending on the stimulus, task, and context—in fact, the neural loci that are involved in the analysis of the stimuli for which priming effects are seen.     

Local processes in preattentive feature detection.

Sagi and Julesz (1987) claimed that for a target to be detected preattentively, it must be within some small critical distance of a nontarget. The independent effects of separation and display size, which were confounded in the Sagi and Julesz experiments, were examined. Experiments 1 and 2 revealed that in tasks requiring search for a color-defined target, target-nontarget separation had no effect on reaction time (RT). Display size, however, was inversely related to RT. Experiment 3 ruled out the possibility that the decreasing function of RT with display size was due to arousal caused by higher display luminance. When nontarget grouping was inhibited, (Exp. 4) it was found that RT no longer decreased with increasing display size. This suggests that nontarget grouping may have been the cause of the improved performance at larger display sizes. Experiments 5 and 6 extended the results to line segments, the stimuli used by Sagi and Julesz.     

Characteristics and models of human symmetry detection

Symmetry is everywhere - in natural objects, from crystals to living organisms, in manufactured articles of many kinds, and in art works from all cultures. Symmetry is a salient visual property that is detected efficiently and rapidly by the human visual system. In this paper, several decades of experimental research on human symmetry detection are reviewed. By examining the effects of several factors on symmetry detection, this research has revealed some important characteristics of how humans perceive symmetry. These characteristics constrain the general principles of putative underlying mechanisms and models of human symmetry detection. For example, the orientation of the axis of symmetry and its location in the visual field have effects that suggest that the bilateral symmetry of the visual system at cortical levels of the brain might partly determine the salience of vertical mirror symmetry. At the same time, there is a surprisingly high degree of flexibility and robustness that remains to be explained. Thus, symmetry provides a major challenge to model human flexibility and efficiency within the constraints of the biology of the visual system.     

Do locally defined feature discontinuities capture attention?

Results from previous visual search studies have suggested that abrupt onsets produce involuntary shifts of attention (i.e., attentional capture), but discontinuities in simple features such as color and brightness do not (Jonides & Yantis, 1988). In the present study we tested whether feature discontinuities (i.e., “singletons”) can produce attentional capture in a visual search task if defined “locally” or over a small spatial range. On each trial, a variable number of letters appeared, one of which differed from the others in color or intensity. The location of this singleton was uncorrelated with target location. Local discontinuities were created by embedding the letters in a dot texture. In Experiment 1, display size effects for singleton targets were not reduced with the addition of a background dot texture. Similar results were obtained in Experiment 2, regardless of variations in texture density. Experiment 3 confirmed that when targets are defined by a color or intensity singleton, they are detected preattentively, and that increasing texture density yields faster detection. We conclude that the spatial range over which feature discontinuities are defined may influence the guidance of spatial attention, but it has no influence on their ability to capture attention.     

Grouping does not require attention

Many theories of visual perception stipulate that Gestalt grouping occurs preattentively. Subjects' failure to report perceiving even salient grouping patterns under conditions of inattention challenges this assumption (see, e.g., Mack, Tang, Tuma, Kahn, & Rock, 1992), but Moore and Egeth (1997) showed that although subjects are indeed unable to identify grouping patterns outside the focus of attention, effects of these patterns on visual perception can be observed when they are assessed using implicit, rather than explicit, measures. However, this finding, which is the only one to date demonstrating grouping effects without attention, is open to an alternative account. In the present study, we eliminated this confound and replicated Moore and Egeth's findings, using the Müller-Lyer illusion (Experiments 1 and 2). Moreover, we found converging evidence for these findings with a variant of the flanker task (Experiment 3), when the amount of available attentional resources was varied (Experiments 4 and 5). The results reinforce the idea that, although grouping outside the focus of attention cannot be the object of overt report, grouping processes can occur without attention.     

Effects of surface pre-presentation on symmetry detection on a 3-D bumpy surface

Abstract:  The aim of this study was to investigate the visual detection mechanism of mirror symmetrical dot patterns drawn on a 3-D bumpy surface (i.e., 3-D noisy curved surface). The focus of this investigation was whether symmetry detection on the bumpy surface is associated with structure recovery of the surface. In Experiment 1, we confirmed that the human visual system can distinguish the bumpy surface from a distorted dot pattern on a transparent bumpy surface. In Experiment 2, we required participants to discriminate between a symmetrical pattern on a transparent (non-visible) bumpy surface and an opaque (visible) bumpy surface for the same stimuli as in Experiment 1. Finally, in Experiment 3, we examined the effect of pre-presentation of the opaque bumpy surface on pattern discrimination. The results showed that pre-presentation of the opaque surface facilitated the detection of a diagonal symmetry, but not in the case of the detection of a cardinal symmetry. These results suggested that diagonal symmetry involves the process of surface recovery, whereas cardinal symmetry does not.     

The role of visible persistence for perception of visual bilateral symmetry1

Abstract: Although the detection of visual bilateral symmetry has been claimed to be highly efficient, the possible involvement and function of visual memory in such efficient mechanisms has rarely been examined. We hypothesized that symmetry perception is rapid, as it can be achieved from rapidly decaying information of visible persistence. To test this hypothesis, we employed a temporal integration paradigm. A symmetric dot pattern was randomly divided into two asymmetric patterns and presented successively with a blank screen presented between patterns. Observers could detect symmetry when the two patterns were presented close in time (Experiment 1), indicating that observers perceived symmetry presumably utilizing visible persistence. In addition, the inverse‐intensity effect of visible persistence (Di Lollo & Bischof, 1995) was evident in our temporal integration task of symmetry (Experiment 2). The results of the current study clearly demonstrate that the detection of symmetry can be achieved based on the visible persistence. The large capacity and high spatial precision of visible persistence might be adequate for the rapid and spatially global encoding of visual symmetry.     

Changes are not localized before they are explicitly detected

Change detection is in many ways analogous to visual search. Yet, unlike search, successful detection depends not on the salience of features within a scene, but on the difference between the original and modified scene. If, as in search, pre-attentive mechanisms guide attention to the change location, the change itself must produce a preattentively detectable signal. Despite recent evidence for implicit representation of change in the absence of conscious detection, few studies have yet explored whether attention is guided to a change location prior to explicit detection. In four “change blindness” experiments using several variants of the “flicker” task, we tested the hypothesis that implicit or preattentive mechanisms guide change localization prior to explicit detection. None of the experiments revealed improved localization of changes prior to explicit reports of detection, suggesting that implicit detection of change does not contribute to the eventual explicit localization of a change. Instead, change localization is essentially arbitrary, driven by the salience of features within scenes.     

Visual attention and perceptual grouping

Perceptual organization is thought to involve an analysis of bothtextural discontinuities andperceptual grouping. In earlier work, we found that textural discontinuities were detected normally even when visual attention was engaged elsewhere. Here we report how perceptual grouping is affected when visual attention is engaged by a concurrent visual task. To elicit perceptual grouping, we used the Gestalt demonstrations of grouping on the basis of proximity and of similarity. Four tasks were investigated, some requiring the observer to discriminate between horizontal and vertical grouping, and some requiring the observer to merely detect the presence or absence of grouping. Visual attention was engaged at the center of the display by a form identification task. The detection of a textural discontinuity served as a control task. Concurrent form identification conflicted with all four grouping tasks, resulting in a significant reduction of grouping performance in each case. No performance reduction was observed when either form identification or grouping discrimination was combined with the detection of a textural discontinuity. These results suggest that perceptual grouping and form identification compete for visual attention, whereas the detection of a textural discontinuity does not.     

Visual symmetry perception in early onset monocular blindness

Symmetry detection is impaired by abnormal binocular vision development such as in amblyopia. However, the detection of symmetry has never been investigated in cases where input from one eye is profoundly compromised. Testing monocularly blind (MB) individuals represents a unique opportunity to investigate whether symmetry salience relies on a normally developed binocular visual system. In a visual symmetry detection task using dot patterns, congenitally MB showed comparable accuracy to normally sighted individuals viewing monocularly. This included better detection of vertically than horizontally symmetric patterns. However, the MB were slower than controls in detecting a symmetrical pattern. In a control target-detection task, no significant differences in performance were observed between these groups. Overall, normal developing binocular vision does not appear necessary for the visual system to detect the presence of visual symmetry. However, optimal detection mechanisms may be dependent on binocular summation or other processes dependent on input from both eyes.     

Does prior knowledge facilitate the detection of visual targets in random noise?

The detectability of forms embedded within random visual noise has been found to be predictable from the autocorrelation transform of the stimulus pattern (Uttal, 1975). A basic assumption in the autocorrelation theory of form detection is that detectability is determined by the organization of the stimulus pattern, irrespective of the observer’s prior knowledge or expectations about the characteristics of the form. This assumption was tested by determining the effect of the size of the set of alternative target forms on performance of a forced-choice detection task. The targets were composed of dots in a straight line, appearing in one of a specified set of 2, 4, or 8 alternative positions in a pattern of randomly distributed masking dots. Detection accuracy was found to decrease as set size increased, but this decrease was close to what was predicted on the assumption that the random background was independently confusable with the target at each of the alternative positions. Thus, prior knowledge of the set of alternative targets appeared to have no effect on thevisual process, but only on thedecision process by virtue of the features that were relevant criteria for deciding which of the two patterns on each trial was most likely to contain the target. This result is consistent with the autocorrelation theory. This experiment may illustrate how the decision process has influenced the performance in many other experiments that have been assumed to demonstrate an effect of prior knowledge on perception.     

Feature integration that routinely occurs without focal attention

To analyze visual scenes, the visual system decomposes the visual scene into features that are processed in parallel by separate subsystems. Certain theories (Treisman, Wolfe) propose that these subsystems function independently before focal attention integrates their output. We describe a new paradigm—the gestalt detection task—that directly assesses the degree of preattentive dependence between any two subsystems. We present five experiments that test whether the subsystems that process form and color function independently in processing brief (and, therefore, preattentively processed) stimuli. Our data show that these two subsystems interact during the preattentive processing of featuredependent information. They are synergistic when the information they receive is consistent; they are antagonistic when the information they receive is inconsistent.     

Facilitated detection of angry faces: Initial orienting and processing efficiency

In a visual search task, displays of four schematic faces (angry, sad, happy, or neutral) were presented. Participants decided whether the faces were all the same or whether one was different. A discrepant angry face in a context of three neutral faces was detected faster than other faces. This occurred in the absence of a higher probability of first fixation on the angry face. Moreover, angry faces were more accurately detected even when presented parafoveally. These results are not consistent with the hypothesis that angry faces are detected faster because they are looked at earlier. In contrast, angry faces were looked at less than other faces during the search process and were more accurately detected than other faces when the display duration was reduced to 150 ms. These results support the processing efficiency hypothesis, according to which fewer attentional resources are needed to identify angry faces, which would account for their speeded detection time. In addition, parafoveal analysis of the angry faces may start preattentively, which would account for the fewer and shorter fixations that they need later, when they come under the focus of attention.     

The role of contour polarity,objectness, and regularities in haptic and visual perception

Regularities like symmetry (mirror reflection) and repetition (translation) play an important role in both visual and haptic (active touch) shape perception. Altering figure-ground factors to change what is perceived as an object influences regularity detection. For vision, symmetry is usually easier to detect within one object, whereas repetition is easier to detect across two objects. For haptics, we have not found this interaction between regularity type and objectness (Cecchetto & Lawson, Journal of Experimental Psychology: Human Perception and Performance, 43, 103–125, 2017; Lawson, Ajvani, & Cecchetto, Experimental Psychology, 63, 197–214, 2016). However, our studies used repetition stimuli with mismatched concavities, convexities, and luminance, and so had mismatched contour polarities. Such stimuli may be processed differently to stimuli with matching contour polarities. We investigated this possibility. For haptics, speeded symmetry and repetition detection for novel, planar shapes was similar. Performance deteriorated strikingly if contour polarity mismatched (keeping objectness constant), whilst there was a modest disadvantage for between-2objects:facing-sides compared to within-1object:outer-sides comparisons (keeping contour polarity constant). For the same task for vision, symmetry detection was similar to haptics (strong costs for mismatched contour polarity, weaker costs for between-2objects:facing-sides comparisons), but repetition detection was very different (weak costs for mismatched contour polarity, strong benefits for between-2objects:facing-sides comparisons). Thus, objectness was less influential than contour polarity for both haptic and visual symmetry detection, and for haptic repetition detection. However, for visual repetition detection, objectness effects reversed direction (within-1object:outer-sides comparisons were harder) and were stronger than contour polarity effects. This pattern of results suggests that regularity detection reflects information extraction as well as regularity distributions in the physical world.     

Feature confirmation in object perception: Feature integration theory 26 years on from the Treisman Bartlett lecture

The Treisman Bartlett lecture, reported in the Quarterly Journal of Experimental Psychology in 1988, provided a major overview of the feature integration theory of attention. This has continued to be a dominant account of human visual attention to this day. The current paper provides a summary of the work reported in the lecture and an update on critical aspects of the theory as applied to visual object perception. The paper highlights the emergence of findings that pose significant challenges to the theory and which suggest that revisions are required that allow for (a) several rather than a single form of feature integration, (b) some forms of feature integration to operate preattentively, (c) stored knowledge about single objects and interactions between objects to modulate perceptual integration, (d) the application of feature-based inhibition to object files where visual features are specified, which generates feature-based spreading suppression and scene segmentation, and (e) a role for attention in feature confirmation rather than feature integration in visual selection. A feature confirmation account of attention in object perception is outlined.