Tuesday, November 29, 2016

Quick takes: detect animate vs. inanimate in 250 msec

Back in the 1970s & 1980s David Hays and I hypothesized the existence of perceptual mechanisms that would support a quick determination of whether or not something was alive. We figured such perception would have survival value as knowing whether you're facing an animate being or not could mean life or death in the wild. Well, now we know:

In PsyPost:
UC Berkeley scientists have discovered a visual mechanism they call “ensemble lifelikeness perception,” which determines how we perceive groups of objects and people in real and virtual or artificial worlds.

“This unique visual mechanism allows us to perceive what’s really alive and what’s simulated in just 250 milliseconds,” said study lead author Allison Yamanashi Leib, a postdoctoral scholar in psychology at UC Berkeley. “It also guides us to determine the overall level of activity in a scene.”

Vision scientists have long assumed that humans need to carefully consider multiple details before they can judge if a person or object is lifelike.

“But our study shows that participants made animacy decisions without conscious deliberation, and that they agreed on what was lifelike and what was not,” said study senior author David Whitney, a UC Berkeley psychology professor. “It is surprising that, even without talking about it or deliberating about it together, we immediately share in our impressions of lifelikeness.” [...]

Moreover, if we did not possess the ability to speedily determine lifelikeness, our world would be very confusing, with every person, animal or object we see appearing to be equally alive, Whitney said.
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Fast ensemble representations for abstract visual impressions

Allison Yamanashi Leib, Anna Kosovicheva & David Whitney
Nature Communications 7, Article number: 13186 (2016) doi:10.1038/ncomms13186
Published online: 16 Nov. 2016


Much of the richness of perception is conveyed by implicit, rather than image or feature-level, information. The perception of animacy or lifelikeness of objects, for example, cannot be predicted from image level properties alone. Instead, perceiving lifelikeness seems to be an inferential process and one might expect it to be cognitively demanding and serial rather than fast and automatic. If perceptual mechanisms exist to represent lifelikeness, then observers should be able to perceive this information quickly and reliably, and should be able to perceive the lifelikeness of crowds of objects. Here, we report that observers are highly sensitive to the lifelikeness of random objects and even groups of objects. Observers’ percepts of crowd lifelikeness are well predicted by independent observers’ lifelikeness judgements of the individual objects comprising that crowd. We demonstrate that visual impressions of abstract dimensions can be achieved with summary statistical representations, which underlie our rich perceptual experience.

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From the conclusion:

Our findings reveal that ensemble perception of lifelikeness is achieved extremely rapidly. While previous work has shown that observers categorize stimuli in a brief time period (for example, animal or non- animal34,35), our study shows that observers can perceive relative lifelikeness (that is, whether one stimulus is more life-like than another) on a similarly rapid timescale for groups as well. These results parallel the rapid time scale reported in previous ensemble coding experiments using stimuli with explicit physical dimensions24,26, highlighting the remarkable efficiency of ensemble representations that support abstract visual impressions.

Our findings suggest that lifelikeness is an explicitly coded perceptual dimension that is continuous as opposed to dichot- omous. One prior study has investigated whether animacy is a strictly dichotomous representation, or whether animacy is represented as a continuum36. While this prior study focused on single repeated stimuli shown for longer exposure durations, our findings extend this question to groups of heterogeneous objects that were briefly presented. Our participants extracted a graded ensemble percept of group lifelikeness. Because of the rapid timescale, the judgements of lifelikeness in our experiment would not allow for cognitive reasoning or social processes. Consistent with this, explicit memory of the objects in the sets was not sufficient to account for the number of objects integrated into the ensemble percept. Our results suggest that graded representations of object and crowd lifelikeness emerge as a basic, shared visual percept, available during rudimentary and rapid visual analysis of scenes.

Animacy, as a general construct and topic of cognition research, is extremely complex. Numerous contextual, cognitive and social mechanisms come into play when determining whether an object exhibits animate qualities. Specifically, when making judgements about animacy, theory of mind37–39, contextual cues40,41 and cognitive strategies42 contribute significantly to animacy evaluations. These complexities help explain why there are relatively few agreed-upon operational definitions of animacy or lifelikeness.

In contrast to the ambiguity of the terms animacy or lifelikeness, our results show that the ensemble perception of lifelikeness in groups of static objects was surprisingly consistent across observers. When stimuli were presented for brief durations, observers reached a remarkable consensus on the average lifelikeness—even regarding objects that exhibit seemingly ambiguous qualities. This consistency suggests that a similar percept of lifelikeness is commonly available to observers who glance at a scene. Numerous cognitive and social mechanisms may come online later, and observers may refine their percepts of lifelikeness when given longer periods to evaluate items and context. However, in a first-glance impression of the environment, observers share a relatively unified, consistent percept of lifelikeness.

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