2007

Holistic crowding: selective interference between configural representations of faces in crowded scenes.

In this study, we investigated whether crowding could occur selectively among upright faces. We found that subjects' performance was worse when a target face was surrounded by upright flanker faces than when the target face was surrounded by inverted flanker faces or no faces at all. These results demonstrate that in addition to low-level featural crowding, crowding can occur selectively between high-level (configural) representations of faces, suggesting that crowding may occur at multiple stages in the visual system.

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Rapid extraction of mean emotion and gender from sets of faces.

We frequently encounter crowds of faces. Here we report that, when presented with a group of faces, observers quickly and automatically extract information about the mean emotion in the group. This occurs even when observers cannot report anything about the individual identities that comprise the group. The results reveal an efficient and powerful mechanism that allows the visual system to extract summary statistics from a broad range of visual stimuli, including faces.

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Position shifts following crowded second order motion adaptation reveal processing of local and global motion without awareness.

Adaptation to first-order (luminance defined) motion produces not only a motion aftereffect but also a position aftereffect, in which a target pattern's perceived location is shifted opposite the direction of adaptation. These aftereffects can occur passively (when the direction of motion adaptation cannot be detected) and remotely (when the target is not at the site of adaptation). Although second-order (contrast defined) motion produces these aftereffects, it is unclear whether they can occur passively or remotely. To address these questions, we conducted two experiments. In the first, we used crowding to remove a local adapter's second-order motion from awareness and still found a significant position aftereffect. In the second experiment, we found that the direction of motion in one region of a crowded array could produce a position aftereffect in an unadapted, spatially separated region of the crowded array. The results suggest that second-order motion influences perceived position over a large spatial range even without awareness.

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Second-order motion without awareness: passive adaptation to second-order motion produces a motion aftereffect.

Although second-order motion may be detected by early and automatic mechanisms, some models suggest that perceiving second-order motion requires higher-order processes, such as feature or attentive tracking. These types of attentionally mediated mechanisms could explain the motion aftereffect (MAE) perceived in dynamic displays after adapting to second-order motion. Here we tested whether there is a second-order MAE in the absence of attention or awareness. If awareness of motion, mediated by high-level or top-down mechanisms, is necessary for the second-order MAE, then there should be no measurable MAE if the ability to detect directionality is impaired during adaptation. To eliminate the subject's ability to detect directionality of the adapting stimulus, a second-order drifting Gabor was embedded in a dense array of additional crowding Gabors. We found that a significant MAE was perceived even after adaptation to second-order motion in crowded displays that prevented awareness. The results demonstrate that second-order motion can be passively coded in the absence of awareness and without top-down attentional control.

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2005

Motion distorts perceived position without awareness of motion.

To view a Quicktime demo of the stimuli, click on the image above. Fixate on the bull's-eye on the left of the screen and notice the array of drifting patches in your periphery. While fixating, if you try to judge the direction of motion in the patch that is three from the left and two from the top of the array, you'll find it is extremely difficult. Continue fixating on the bull's-eye and notice that the two single patches, presented during the test period, look misaligned (and may appear to move). Those two test patches are physically static and physically aligned. The illusory misalignment is caused by motion adaptation that was crowded out of your awareness. Observers are not able to distinguish the direction of motion in the central patches, but the exposure to that motion influences subsequent judgments of object location. This demonstrates that the visual system's passive motion detection mechanisms influence the coding of object location.

A number of striking illusions show that visual motion influences perceived position [1];in all of these, the perceived shift is accompanied or preceded by a visible and salient motion signal. Observers can easily scrutinize the motion: they can attentively track, or at least perceive via inference, the moving features [2, 3 and 4]. With position shifts that accompany the motion aftereffect (MAE) [5, 6, 7, 8, 9 and 10], for example, observers can attentively track the moving adaptation stimulus [11 and 12]. Even if the shifted test pattern does not display any perceived motion [6 and 10], the moving adaptation stimulus is clearly visible, and it could be the visibility of the adaptation stimulus that causes the perceived shift in the test stimulus position. If awareness of motion, mediated by high-level or top-down mechanisms, explains all motion-induced position shifts, then there should be no shift in perceived position without the perception of directional motion. Here, we show that perceived position can be shifted even without awareness of motion.

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