Shaul Hochstein

Hebrew University of Jerusalem | HUJI · Edmond and Lily Safra Center for Brain Sciences

Visual scenes are too complex for one to immediately perceive all their details. As suggested by Gestalt psychologists, grouping similar scene elements and perceiving their summary statistics provides one shortcut for evaluating scene gist. Perceiving ensemble statistics overcomes processing, attention, and memory limits, facilitating higher-order...

Ensemble perception refers to the visual system's ability to efficiently represent groups of similar objects as a unified percept using their summary statistical information. Most studies focused on extraction of current trial averages, giving little attention to prior experience effects, although a few recent studies found that ensemble mean estim...

This Element outlines the recent understanding of ensemble representations in perception in a holistic way aimed to engage the general audience, novel and expert alike. The Element highlights the ubiquitous nature of this summary process, paving the way for a discussion of the theoretical and cortical underpinnings, and why ensemble encoding should...

Visual search has been classified as easy feature search, with rapid target detection and little set size dependence, versus slower difficult search with focused attention, with set size-dependent speed. Reverse hierarchy theory attributes these classes to rapid high cortical-level vision at a glance versus low-level vision with scrutiny, attributi...

Perception, representation, and memory of ensemble statistics has attracted growing interest. Studies found that, at different abstraction levels, the brain represents similar items as unified percepts. We found that global ensemble perception is automatic and unconscious, affecting later perceptual judgments regarding individual member items. Impl...

Previous studies have demonstrated a complex relationship between ensemble perception and outlier detection. We presented two array of heterogeneously oriented stimulus bars and different mean orientations and/or a bar with an outlier orientation, asking participants to discriminate the mean orientations or detect the outlier. Perceptual learning w...

Anne Treisman investigated many aspects of perception, and in particular the roles of different forms of attention. Four aspects of her work are reviewed here, including visual search, set mean perception, perception in special populations, and binocular rivalry. The importance of the breakthrough in each case is demonstrated. Search is easy or slo...

A bombardment of information overloads our sensory, perceptual and cognitive systems, which must integrate new information with memory of past scenes and events. Mechanisms employed to overcome sensory system bottlenecks include selective attention, Gestalt gist perception, categorization, and the recently investigated ensemble encoding of set summ...

Two cognitive processes have been explored that compensate for the limited information that can be perceived and remembered at any given moment. The first parsimonious cognitive process is object categorization. We naturally relate objects to their category, assume they share relevant category properties, often disregarding irrelevant characteristi...

Visual scenes are too complex to perceive immediately in all their details. Two strategies (among others) have been suggested as providing shortcuts for evaluating scene gist before its details: (a) Scene summary statistics provide average values that often suffice for judging sets of objects and acting in their environment. Set summary perception...

To compensate for the limited visual information that can be perceived and remembered at any given moment, many aspects of the visual world are represented as summary statistics. We acquire ensemble representations of element groups as a whole, spreading attention over objects, for which we encode no detailed information. Previous studies found tha...

The new “eyes wide shut” illusion uses a standard enlarging (shaving or makeup) mirror. Close one eye and look at the closed eye in the mirror; the eye should take up most of the mirror. Switch eyes to see the other closed eye. Switch back-and-forth a few times, then open both eyes. You see an open eye. Which eye is it? To find out, close one eye....

Background: Patients with Balint syndrome following bilateral parietal damage are typically described as being unable to perceive multiple objects simultaneously, preventing them from understanding the visual scene despite correct identification of individual visual objects (simultanagnosia). We report observations with DP, a patient with a rare st...

Introduction. Much recent interest has been directed at perception of summary statistics. As discussed in a variety of presentations at this and previous VSS meetings, intensive research has uncovered diverse dimensions of summary statistic perception, including simple and complex dimensions (from circle size and Gabor orientation to face emotion a...

Are memory capabilities of humans and monkeys similar or does one species have superior abilities? In particular, does language afford better memory facilities? We compared monkey and human memory capabilities in a delay-match-to-multiple-item memory task. In each trial, a series of samples was presented and participants detected and responded to a...

The syndrome of unilateral spatial neglect (USN) after right-hemisphere damage is characterized by failure of salient left-sided stimuli to activate an orienting response, attract attention, and gain access to conscious awareness. The explicit failure processing left-sided visual information is not uniform, however, and patients seem to be more suc...

In the framework of Reverse Hierarchy Theory it was suggested that initial vision at a glance brings the gist of the scene to conscious perception using explicit high cortical level representations, which are initially built by implicit bottom-up processing (Hochstein & Ahissar, 2002). Only later return to lower cortical level representations intro...

The Delay-Match-to-Sample (DMS) task has been used in countless studies of memory, undergoing numerous modifications, making the task more and more challenging to participants. The physiological correlate of memory is modified neural activity during the cue-to-match delay period reflecting reverberating attractor activity in multiple interconnected...

Delay match to sample (DMS) experiments provide an important link between the theory of recurrent network models and behavior and neural recordings. We define a simple recurrent network of binary neurons with stochastic neural dynamics and Hebbian synaptic learning. Most DMS experiments involve heavily learned images, and in this setting we propose...

What happens to cross-modal perceptual resources when task performance is predictably poor? This question is central for understanding the efficiency of attention allocation among concurrent tasks in different modalities and for assigning multi-tasking operations in real-life situations (such as texting while driving a car). General load theories p...

We are studying familiarity memory (knowing that I have seen this image somewhere. sometime before) and identification memory (knowing where and when I saw it, and perhaps its name). We now address memory decay in these conditions, including cases when forgetting is desirable. We introduce a multiple-item memory task, where subjects report repetiti...

Reviewing the current literature, one finds physiological bases for Gestalt-like perception, but also much that seems to contradict the predictions of this theory. Some resolution may be found in the framework of Reverse Hierarchy Theory, dividing between implicit processes, of which we are unaware, and explicit representations, which enter percept...

Binocular rivalry (BR) occurs when the brain cannot fuse percepts from the two eyes because they are different. We review results relating to an ongoing controversy regarding the cortical site of the BR mechanism. Some BR qualities suggest it is low-level: (1) BR, as its name implies, is usually between eyes and only low-levels have access to utroc...

Background / Purpose: People rapidly judge mean size of a set of circles, suggesting pre-attentive processing of statistical properties (1). Can neglect patients process statistical properties in their neglected field? Main conclusion: We conclude that neglect patients perform weighted averages across sides, giving partial-weight to left-side,...

According to art theory, pictorial balance acts to unify picture elements into a cohesive composition. For asymmetrical compositions, balancing elements is thought to be similar to balancing mechanical weights in a framework of symmetry axes. Assessment of preference for balance (APB), based on the symmetry-axes framework suggested in Arnheim R, 19...

According to art theory, pictorial balance acts to unify picture elements into a cohesive composition. For asymmetrical compositions, balancing elements is thought to be similar to balancing mechanical weights in a framework of symmetry axes. Assessment of preference for balance (APB), based on the symmetry-axes framework suggested in Arnheim R, 19...

We construct a mathematical model indicating the information available to the observer regarding each item in a spatial unit in the visual scene, at any given moment, dependant on previous fixations and eye movement scanpath. Dividing the items in the visual scene into discrete units, two processes affect the amount of information available about e...

It is well established that cognitive system overload is reflected in the attentional blink (AB), the failure to report a second target when it closely follows detection of a first target within a rapid series of stimuli. However, there is intense controversy concerning the effect of first-target detection in one modality on subsequent dynamics of...

Perceptual learning involves modification of cortical processes so that transfer to new task variants depends on neuronal representation overlap. Neuron selectivity varies with cortical level, so that the degree of transfer should depend on training-induced modification level. We ask how different can stimuli be, how far apart can their representat...

We present a new view of the organization of implicit and explicit mechanisms subserving visual perception. We propose that initial feed-forward processing along the hierarchy of visual cortical areas is implicit, not available to consciousness and not under conscious control. Explicit perception begins at the large generalizing receptive fields of...

It has been a basic tenet of the search literature that only elements that differ in a basic feature such as orientation or color would pop out from an array of distractors. More recent research has shown, however, that high-level concepts may pop out as well. Furthermore, experiments generally used a uniform array of distractors for search tests....

Previously, we found hemispheric differences when testing feature search with arrays wholly in one hemifield (Pavlovskaya et al., Spatial Vision, 2001), rather than testing with central arrays and lateral target elements. In parallel, Ahissar & Hochstein (Nature, 1997) found that perceptual learning transfer across position or orientation depends o...

According to Reverse Hierarchy Theory (Hochstein & Ahissar, Neuron, 2002), high level cortical regions are responsible for pop-out - rapid detection of an element that differs greatly from surrounding elements in a single dimension such as color or orientation. With large-receptive field attention spread across the entire array, subjects detect pre...

Faces are detected more rapidly than other objects in visual scenes and search arrays, but the cause for this face advantage has been contested. In the present study, we found that under conditions of spatial uncertainty, faces were easier to detect than control targets (dog faces, clocks and cars) even in the absence of surrounding stimuli, making...

Chong and Treisman (2003, 2005, 2008) found that people judge the mean size of a set of circles as quickly and accurately as that of a single item, suggesting that statistical properties may be processed without focused attention. The lack of awareness of left-side input in cases of Unilateral Spatial Neglect (USN) has been attributed to an inabili...

While it is quite evident that we are not aware of all cortical activity, evidence is still sparse concerning what unconscious information is usable for task performance. The famous case of Blindsight underscores the importance of this issue - in brains with specific damage. We present three cases of the use of information of which (healthy) partic...

Even when our attention is dedicated to an important task, background processes monitor the environment for significant events. The mismatch negativity (MMN) event-related potential is thought to reflect such a monitoring process. Nevertheless, there is continuing debate concerning the susceptibility of the MMN to attentional manipulation. We inves...

Encountering someone on the street, we can often say whether their face is familiar, though it may be difficult to identify the person: Familiarity memory may differ essentially from identification, which embeds and generates contextual information. We studied multiple stimulus memory in macaque monkeys using a modified delayed-match-to-sample task...

Category learning is a fundamental cognitive process enabling the creation of simplified representations of objects/events. We focus on comparison processes for category learning - learning categories by comparing pairs of exemplars identified to be from the same category (same-class exemplars) vs. pairs from different categories (different-class e...

Findings from numerous studies suggest that multiple neural systems are involved in category learning. Specifically, it is often argued that acquiring a representation of different category structures (e.g., rule-based vs. prototype-based representation) involves different computational challenges, which are resolved by different neural circuitries...

Target recognition stages were studied by exposing observers to varying controlled numbers of target fixations. The target, present in half the displays, consisted of two identical cards (Identity Search Task; Jacob & Hochstein, 2009). Following more fixations, targets are better recognized, indicated by increased Hit-rate and detectability (accord...

Background: Differences in perceptual learning transfer may be related to the cerebral sites of modification due to experience: hard-condition tasks are seen as requiring low-level (specific) representations while easy-condition tasks are performed using high cortical level mechanisms alone (Ahissar & Hochstein, Nature, 1997). As an example, we rec...

Background: According to Reverse Hierarchy Theory (Ahissar & Hochstein, Nature, 1997; Hochstein & Ahissar, Neuron, 2002), rapid conscious vision reflects a high-level cortical representation. This permits implicit integration of multiple spatially separated stimulus elements and direct perception of complex forms on the basis of what must be called...

Two observers looking at the same picture may not see the same thing. To avoid sensory overload, visual information is actively selected for further processing by bottom-up processes, originating within the visual image, and top-down processes, reflecting the motivation and past experiences of the observer. The latter processes could grant categori...

Information for category learning may be provided as positive or negative equivalence constraints (PEC/NEC)-indicating that some exemplars belong to the same or different categories. To investigate categorization strategies, we studied category learning from each type of constraint separately, using a simple rule-based task. We found that participa...

We investigated explicit and implicit properties of the internal representation of illusory-contour figures by studying potential priming effects of this representation. Using a primed matching paradigm (Beller 1971, Journal of Experimental Psychology 87 176-182), we found that illusory 'Kanizsa' squares and triangles prime later matching of the sa...

Category learning can be achieved by identifying common features among category members, distinctive features among non-members, or both. These processes are psychologically and computationally distinct, and may have implications for the acquisition of categories at different hierarchical levels. The present study examines an account of children's...

Why do we perceive some elements in a visual scene, while others remain undetected? To learn about the sequence of events leading to detection, we directly compared fixations on detected vs. undetected items. Our novel Identity Search task display comprised twelve cards, all different except for two pairs of identical cards. Participants search for...

Revealing the relationships between perceptual representations in the brain and mechanisms of adult perceptual learning is of great importance, potentially leading to significantly improved training techniques both for improving skills in the general population and for ameliorating deficits in special populations. In this review, we summarize the e...

The Set visual perception game is a fertile research platform that allows investigation of perception, with gradual processing culminating in a momentary recognition stage, in a context that can be endlessly repeated with novel displays. Performance of the Set game task is a play-off between perceptual and conceptual processes. The task is to detec...

We previously found a dominant eye perceptional advantage in feature search (Vision Research, 2006). We now ask if this advantage extends to difficult conjunction search, which requires focused attention and depends on different cortical hierarchy levels. We determined eye dominance by the Hole-in-the-Card test. Using red-green glasses, subjects vi...

Recent studies stressed the importance of comparing exemplars both for improving performance by artificial classifiers as well as for explaining human category-learning strategies. In this report we provide a theoretical analysis for the usability of exemplar comparison for category-learning. We distinguish between two types of comparison -- compar...

We investigate the relationship between illusory figure detection and discrimination of its shape, asking whether these depend on a single, two separate, or two sequential processes. In a simultaneous detection-discrimination experiment, we presented subjects with brief, backward-masked Kanizsa-type patterns consisting of four "pacmen," arranged as...

Macaque monkeys were tested on a delayed-match-to-multiple-sample task, with either a limited set of well trained images (in randomized sequence) or with never-before-seen images. They performed much better with novel images. False positives were mostly limited to catch-trial image repetitions from the preceding trial. This result implies extremely...

Classification tasks are often based on training with labeled exemplars. This paradigm, as others, presents classi- fiers with two types of information: that pairs of objects belong to the same class (Positive Equivalence Constraints or PECs) or to different classes (Negative Equivalence Constraints or NECs). We now test classification separately w...

We tested the efficiency of category learning when participants are provided only with pairs of objects, known to belong either to the same class (Positive Equivalence Constraints or PECs) or to different classes (Negative Equivalence Constraints or NECs). Our results in a series of cognitive experiments show dramatic differences in the usability o...

We find a spatially asymmetric allocation of attention in patients with traumatic brain injury (TBI) despite the lack of obvious asymmetry in neurological indicators. Identification performance was measured for simple spatial patterns presented briefly to a locus 5 degrees into the left or right hemifield, after precuing attention to the same (ipsi...

We found spatially asymmetric allocation of attention in patients with traumatic brain injury (TBI) without overt asymmetry on neurological examination. The possible effect of Methylphenidate in reducing this asymmetry is evaluated in the current research. Psychophysical study using a visual spatial attention task. Identification rates were measure...

SYNOPSIS Positive phototaxis was demonstrated in specimens of Amphistegina radiata within the range of photonic fluxes of 10 ¹¹ to 10 ¹⁵ photons × cm ‐2 × sec ‐1 . No response was found at lower intensities. Amphistegina radiata has a Dartnall nomogram‐shaped action spectrum with a peak at ∼500 nm. In addition, A. radiata and A. madagascariensis ,...

We studied the role of eye dominance in non-rivalry conditions, testing dichoptic visual search and comparing performance with target presented to the dominant or non-dominant eye. Using red-green glasses, subjects viewed an array of green and red lines of uniform orientation, with a differently oriented target line present on half the trials. Perf...

In this issue of Vision Research, VanRullen, R. (2006). On second glance: Still no high-level pop-out effect for faces. Vision Research, in press. challenges our earlier Vision Research paper, "At first sight: A high-level pop-out effect for faces" (Hershler, O., & Hochstein, S. (2005). At first sight: A high-level pop-out effect for faces. Vision...

What mechanism underlies serial order memory? Studying preverbal serial memory shows that macaque monkeys reproducing a sequence of items can acquire knowledge of item ordinal position. In our previous experiment, macaques were repeatedly presented with image lists (first shown sequentially and then simultaneously on a touch screen together with a...

What mechanism underlies serial order memory? Studying preverbal serial memory shows that macaque monkeys reproducing a sequence of items can acquire knowledge of item ordinal position. In our previous experiment, macaques were repeatedly presented with image lists (first shown sequentially and then simultaneously on a touch screen together with a...

While it is clear that one eye is visually dominant, the function of dominance, if any, is not fully understood. We looked for effects of eye dominance on visual feature search, the easy task of detecting an element that differs significantly in a single dimension from surrounding distractors. Thirteen subjects were tested, each with similar visual...

We investigated human category learning from partial information provided as equivalence constraints. Participants learned to classify stimuli on the basis of either positive or negative equivalence constraints, that is, when informed that two exemplars belong to the same category or to different categories, respectively. Knowing that in natural co...

To determine the nature of face perception, several studies used the visual search paradigm, whereby subjects detect an odd target among distractors. When detection reaction time is set-size independent, the odd element is said to "pop out", reflecting a basic mechanism or map for the relevant feature. A number of previous studies suggested that sc...

We investigate human category learning from partial information pro-vided by equivalence constraints. Human participants learned to classify stimuli on the basis of either positive or negative equivalence constraints, that is, when informed that two exemplars belong to the same category or to different categories, respectively. We discovered that w...