Albrecht, A. R., Scholl, B. J., & Chun, M. M. (2011). Perceptual averaging by eye and ear: Computing visual and auditory summary statistics from multimodal stimuli. Poster presented at the annual meeting of the Vision Sciences Society, 5/10/11, Naples, FL.
Beyond perceiving the features of individual objects, we also have the intriguing ability to efficiently perceive average values of collections of objects across various dimensions -- e.g. the average size of a sequence of discs presented one at a time. Over what features can perceptual averaging occur? Work to date has been limited to visual properties, but perceptual experience is intrinsically multimodal. To find out how perceptual averaging operates in multimodal environments, we explored three questions. First, we asked how well observers can average an auditory feature over time: the changing pitch of a single tone. Not only was auditory averaging robust, but it was more efficient than visual averaging (of the changing size of a disc over time), equating the magnitudes of the changes. Second, we asked how averaging in each modality was influenced by concomitant congruent vs. incongruent changes in the other (task-irrelevant) modality, again combining sizes and pitches. Here we observed a clear and intriguing dissociation. Incongruent visual information hindered auditory averaging, as might be predicted from a simple model of generalized perceptual magnitudes. However, congruent auditory information hindered visual averaging -- perhaps due to a Doppler effect induced by the perception of a disc moving in depth. When modalities are readily separable, you may be able to attend to any modality you choose; but when modalities are readily bound into a cohesive whole, vision may dominate. Finally, we asked about the ability to average both pitch and size simultaneously, and we found very little cost for averaging in either modality when subjects did not know until the end of a trial which average they had to report. These results collectively illustrate that perceptual averaging can span different sensory modalities, and they illustrate how vision and audition can both cooperate and compete for resources.
Gao, T., New, J., & Scholl, B. J. (2011). Perceived biological agency in a Slithering Snake animation. Poster presented at the annual meeting of the Vision Sciences Society, 5/10/11, Naples, FL.
A central task for human vision is to detect the presence of animate agents in the local environment. In studies of perceived animacy, single geometric shapes move in patterns that elicit percepts of animacy and goal-directedness. In studies of biological motion, complex "point-light" body structures engage in highly specialized kinematics that elicit percepts of biological agency. Here we explore a possible midpoint between these phenomena with a novel display -- the Slithering Snake animation -- consisting of a line of small discs, each of which always maintains a short distance from its neighbors. The discs move according to an extremely simple algorithm: the head disc moves randomly, and each subsequent disc moves toward the disc in front of it. This display triggers a rich, compelling percept of snake-like biological agency. We explored the influence of the Slithering Snake on attention and perspective-taking, based on the treatment of the randomly-moving disc as the agent's "head". First, in a probe detection task, we found that attention is automatically attracted to the head (compared with the center, or "tail"). This effect was due to perceived agency, and not to lower-level motion differences or predictability, since the effect (a) reversed when the animations played in reverse order; and (b) largely decreased or even disappeared when the endpoints moved identically, but the snake's middle was invisible or was a rigid line. Second, participants had to quickly identify whether a probe was presented to the left or right of the discs. Responses were slowed considerably when the snake's perspective conflicted with their own (as in a probe to the left of the discs, but to the right from the snake's perspective). These effects show how the perception of biological agency can be generated by surprisingly simple cues, and how such percepts automatically influence other perceptual and cognitive processes.
Liverence, B. M., & Scholl, B. J. (2011). Sustained selective attention warps perceived space: Parallel and opposing effects on attended and inhibited objects. Talk given at the annual meeting of the Vision Sciences Society, 5/9/11, Naples, FL.
Selective attention influences not only which objects in a display are perceived, but also directly changes the character of how they are perceived -- for example making attended objects appear larger or brighter. Here we explore the influence of sustained selective attention on where objects are perceived in relation to each other, in dynamic multi-object displays. Surprisingly, we find that sustained attention warps perceived space in a way that is object-specific: space between targets is perceptually compressed, while space between distractors is perceptually expanded. In an initial multiple object tracking (MOT) task, observers tracked two targets among two distractors. At the end of each trial, however, observers did not click on the target objects, as in typical MOT tasks. Instead, the entire display disappeared, and subjects simply indicated the last perceived location of each object (responding for targets first, followed by distractors). Beyond global spatial compression for the display as a whole, perceived target locations were reported as closer to each other than were perceived distractor locations, in a way that could not be explained by appeal to the response order. We also found similar (and even stronger) object-specific compression effects in a task that did not involve MOT, but simply required sustained monitoring for brief probes in dynamic displays. These effects were specific to targets and distractors per se: factoring out baseline compression toward the center of the display, attended objects seemed to attract each other, while inhibited objects seemed to repel each other. These effects suggest that sustained attention warps perceived space in unexpected ways, and in a manner distinct from previously studied effects of transient attentional shifts.