The Role of Ensemble Statistics in the Visual Periphery

S4 -The Role of Ensemble Statistics in the Visual Periphery

Time/Room: Friday, May 19, 2017, 2:30 – 4:30 pm, Pavilion
Organizer(s): Brian Odegaard, University of California-Los Angeles
Presenters: Michael Cohen, David Whitney, Ruth Rosenholtz, Tim Brady, Brian Odegaard

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The past decades have seen the growth of a tremendous amount of research into the human visual system’s capacity to encode “summary statistics” of items in the world. Studies have shown that the visual system possesses a remarkable ability to compute properties such as average size, position, motion direction, gaze direction, emotional expression, and liveliness, as well as variability in color and facial expression, documenting the phenomena across various domains and stimuli. One recent proposal in the literature has focused on the promise of ensemble statistics to provide an explanatory account of subjective experience in the visual periphery (Cohen, Dennett, & Kanwisher, Trends in Cognitive Sciences, 2016). In addition to this idea, others have suggested that summary statistics underlie performance in visual tasks in a broad manner. These hypotheses open up intriguing questions: how are ensemble statistics encoded outside the fovea, and to what extent does this capacity explain our experience of the majority of our visual field? In this proposed symposium, we aim to discuss recent empirical findings, theories, and methodological considerations in pursuit of answers to many questions in this growing area of research, including the following: (1) How does the ability to process summary statistics in the periphery compare to this ability at the center of the visual field? (2) What role (if any) does attention play in the ability to compute summary statistics in the periphery? (3) Which computational modeling frameworks provide compelling, explanatory accounts of this phenomenon? (4) Which summary statistics (e.g., mean, variance) are encoded in the periphery, and are there limitations on the precision/capacity of these estimates? By addressing questions such as those listed above, we hope that participants emerge from this symposium with a more thorough understanding of the role of ensemble statistics in the visual periphery, and how this phenomenon may account for subjective experience across the visual field. Our proposed group of speakers is shown below, and we hope that faculty, post-docs, and graduate students alike would find this symposium to be particularly informative, innovative, and impactful.

Ensemble statistics and the richness of perceptual experience

Speaker: Michael Cohen, MIT

While our subjective impression is of a detailed visual world, a wide variety of empirical results suggest that perception is actually rather limited. Findings from change blindness and inattentional blindness highlight how much of the huge amounts of the visual world regularly go unnoticed. Furthermore, direct estimates of the capacity of visual attention and working memory reveal that surprisingly few items can be processed and maintained at once. Why do we think we see so much when these empirical results suggests we see so little? One possible answer to this question resides in the representational power of visual ensembles and summary statistics. Under this view, those items that cannot be represented as individual objects or with great precision are nevertheless represented as part of a broader statistical summary. By representing much of the world as an ensemble, observers have perceptual access to different aspects of the entire field of view, not just a few select items. Thus, ensemble statistics play a critical role in our ability to account for and characterize the apparent richness of perceptual experience.

Ensemble representations as a basis for rich perceptual experiences

Speaker: David Whitney, University of California-Berkeley

Much of our rich visual experience comes in the form of ensemble representations, the perception of summary statistical information in groups of objects—such as the average size of items, the average emotional expression of faces in a crowd, or the average heading direction of point-light walkers. These ensemble percepts occur over space and time, are robust to outliers, and can occur in the visual periphery. Ensemble representations can even convey unique and emergent social information like the gaze of an audience, the animacy of a scene, or the panic in a crowd, information that is not necessarily available at the level of the individual crowd members. The visual system can make these high-level interpretations of social and emotional content with exposures as brief as 50 ms, thus revealing an extraordinarily efficient process for compressing what would otherwise be an overwhelming amount of information. Much of what is believed to count as rich social, emotional, and cognitive experience actually comes in the form of basic, compulsory, visual summary statistical processes.

Summary statistic encoding plus limits on decision complexity underlie the richness of visual perception as well as its quirky failures

Speaker: Ruth Rosenholtz, MIT

Visual perception is full of puzzles. Human observers effortlessly per-form many visual tasks, and have the sense of a rich percept of the visual world. Yet when probed for details they are at a loss . How does one explain this combination of marvelous successes and puzzling failures? Numerous researchers have explained the failures in terms of severe limits on resources of attention and memory. But if so, how can one explain the successes? My lab has argued that many experimental results pointing to apparent attentional limits instead derived at least in part from losses in peripheral vision. Furthermore, we demonstrated that those losses could arise from peripheral vision encoding its inputs in terms of a rich set of local image statistics. This scheme is theoretically distinct from encoding ensemble statistics of a set of similar items. I propose that many of the remaining attention/memory limits can be unified in terms of a limit on decision complexity. This decision complexity is difficult to reason about, because the complexity of a given task depends upon the underlying encoding. A complex, general-purpose encoding likely evolved to make certain tasks easy at the expense of others. Recent advances in understanding this encoding — including in peripheral vision — may help us finally make sense of the puzzling strengths and limitations of visual perception.

The role of spatial ensemble statistics in visual working memory and scene perception

Speaker: Tim Brady, University of California-San Diego

At any given moment, much of the relevant information about the visual world is in the periphery rather than the fovea. The periphery is particularly useful for providing information about scene structure and spatial layout, as well as informing us about the spatial distribution and features of the objects we are not explicitly attending and fixating. What is the nature of our representation of this information about scene structure and the spatial distribution of objects? In this talk, I’ll discuss evidence that representations of the spatial distribution of simple visual features (like orientation, spatial frequency, color), termed spatial ensemble statistics, are specifically related to our ability to quickly and accurately recognize visual scenes. I’ll also show that these spatial ensemble statistics are a critical part of the information we maintain in visual working memory – providing information about the entire set of objects, not just a select few, across eye movements, blinks, occlusions and other interruptions of the visual scene.

Summary Statistics in the Periphery: A Metacognitive Approach

Speaker: Brian Odegaard, University of California-Los Angeles

Recent evidence indicates that human observers often overestimate their capacity to make perceptual judgments in the visual periphery. How can we quantify the degree to which this overestimation occurs? We describe how applications of Signal Detection Theoretic frameworks provide one promising approach to measure both detection biases and task performance capacities for peripheral stimuli. By combining these techniques with new metacognitive measures of perceptual confidence (such as meta-d’; Maniscalco & Lau, 2012), one can obtain a clearer picture regarding (1) when subjects can simply perform perceptual tasks in the periphery, and (2) when they have true metacognitive awareness of the visual surround. In this talk, we describe results from recent experiments employing these quantitative techniques, comparing and contrasting the visual system’s capacity to encode summary statistics in both the center and periphery of the visual field.

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