Greg Davis

Seeing other minds: attributed mental states influence perception

A current consensus views social perception as a bottom-up process in which the human brain uses social signals to make inferences about anothers mental state. Here we propose that, contrary to this model, even the most basic perceptual processing of a social stimulus and closely associated automatic responses are modulated by mental-state attribution. We suggest that social perception is subserved by an interactive bidirectional relationship between the neural mechanisms supporting basic sensory processing of social information and the theory-of-mind system. Consequently, processing of a social stimulus cannot be divorced from its representation in terms of mental states. This hypothesis has far-reaching implications for our understanding of both the healthy social brain and characteristic social failures in psychopathology.

Kanizsa Subjective Figures Can Act as Occluding Surfaces at Parallel Stages of Visual Search

Four experiments examined whether Kanizsa subjective figures can induce amodal completion of a notched circle at parallel stages of visual search. Search for the notched circle among full circles was slow and inefficient when the notched circle appeared stereoscopically behind an abutting subjective surface, as if occluded by it. However, search became efficient and parallel when the notched and completed circles appeared nearer so that the subjective figures could not act as occluders. Control studies ruled out explanations in terms of low spatial frequencies, grouping of aligned edges, or the depth of the circles per se. Multiple Kanizsa subjective figures can be coded in parallel as occluding surfaces; such coding is obligatory because it arises even when highly detrimental to performance.

Mental-State Attribution Drives Rapid, Reflexive Gaze Following

When presented with a face stimulus whose gaze is diverted, observers’ attention shifts to locations fixated by the face. Such “gaze following” has been characterized by some previous studies as a consequence of sophisticated theory of mind processes, but by others (particularly those employing the “gaze-cuing” paradigm) as an involuntary response that is triggered directly and reflexively by the physical features of a face. To address this apparent contradiction, we modified the gaze-cuing paradigm using a deception procedure to convince observers that prerecorded videos of an experimenter making head turns and wearing mirrored goggles were a “live” video link to an adjacent room. In two experiments, reflexive gaze following was found when observers believed that the model was wearing transparent goggles and could see, but it was significantly reduced when they believed that the experimenter wore opaque goggles and could not see. These results indicate that the attribution of the mental state “seeing” to a face plays a role in controlling even reflexive gaze following.

Ultra-rapid categorization requires visual attention: Scenes with multiple foreground objects

Human observers can determine whether natural scenes contain an animal or not on the basis of as little as 20 ms viewing; a phenomenon termed ultra-rapid categorization (URC). Recent studies have suggested that URC is unimpaired even when attention resources are concurrently devoted to a second task. This apparent independence of URC from availability of attention resources presents a challenge for the conventional view of high-level vision as attention-demanding. However, one notable feature of the scenes employed in those experiments is that they almost universally comprised only one or two foreground objects. Here, we investigate whether these findings generalize to more complex scenes, more typical of those in nature. We find that categorization of scenes with four primary foreground objects is greatly impaired when attention resources are limited under dual-task conditions, even when scenes are presented for 500 ms. In contrast, URC of scenes with one foreground object is only mildly impaired-the magnitude of this impairment being equivalent to that observed for single objects presented in isolation without naturalistic scene backgrounds. We conclude that URC of complex scenes is particularly attention-dependent but that some attention resources are probably necessary even for URC of simple one-object scenes.

Spreading of Visual Attention to Modally Versus Amodally Completed Regions

Regions of objects that are partially obscured in the current retinal image are often perceptually filled in by the visual system (Kantzsa, 1979) In some cases (modal completion), this causes the filled-in region to appear tinged with the color and brightness of unobscured parts of that object, but in other cases (amodal completion), it does not (Michotte & Burke, 1951) It has recently been argued that modal and amodal completion both arise in preattentive vision, and may operate equivalently at that level (Davis & Driver, 1994, He & Nakayama, 1992, Shipley & Kellman, 1992) In this article, we show that they have different effects on attentive vision, with attention tending to spread to (and from) modally completed regions and their visible inducers, but not to (or from) comparable amodally completed regions and their inducers This finding is consistent with visual attention operating on surfaces (eg, He & Nakayama, 1995) in a viewer-centered representation of the scene, after the operation of filling-in processes.

Perception and apperception in autism: rejecting the inverse assumption.

In addition to those with savant skills, many individuals with autism spectrum conditions (ASCs) show superior perceptual and attentional skills relative to the general population. These superior skills and savant abilities raise important theoretical questions, including whether they develop as compensations for other underdeveloped cognitive mechanisms, and whether one skill is inversely related to another weakness via a common underlying neurocognitive mechanism. We discuss studies of perception and visual processing that show that this inverse hypothesis rarely holds true. Instead, they suggest that enhanced performance is not always accompanied by a complementary deficit and that there are undeniable difficulties in some aspects of perception that are not related to compensating strengths. Our discussion emphasizes the qualitative differences in perceptual processing revealed in these studies between individuals with and without ASCs. We argue that this research is important not only in furthering our understanding of the nature of the qualitative differences in perceptual processing in ASCs, but can also be used to highlight to society at large the exceptional skills and talent that individuals with ASCs are able to contribute in domains such as engineering, computing and mathematics that are highly valued in industry.

The capacity of visual short-term memory is not a fixed number of objects

Luck and Vogel (1997) have reported several striking results in support of the view that visual shortterm memory (VSTM) has a fixed capacity of four objects, irrespective of how many relevant features those objects comprise. However, more recent studies have challenged this account, indicating only a weak effect of the number of objects once other factors are more evenly equated across conditions. Here, we employed a symmetry manipulation to verify object segmentation in our displays, to demonstrate that when spatial and masking factors are held constant, the number of objects per se has no effect on VSTM. Instead, VSTM capacity may reflect the number of object “parts” or feature conjunctions in a given display.

Reversal of object-based benefits in visual attention

In divided-attention tasks, observers must make speeded (or near threshold accuracy) judgements concerning two target features in a display. Typically, when the two features belong to the same object they are more rapidly judged than when they belong to separate objects, a pattern of findings referred to here as a “same-object benefit”. However, we note here that many of these studies share common features, in particular the use of pre-exposed, outline, and/or overlapping objects, and their findings may not generalize to other types of display. Building substantially on previous work by Davis, Welch, Holmes, and Shepherd (2001), we show in four new studies that once these features are not present in a divided-attention task, no same-object benefits are reported. Rather we now find “same-object costs”, where features belonging to a single object are less rapidly judged than features belonging to separate objects.

Object-based attention benefits reveal selective abnormalities of visual integration in autism.

A pervasive integration deficit could provide a powerful and elegant account of cognitive processing in autism spectrum disorders (ASD). However, in the case of visual Gestalt grouping, typically assessed by tasks that require participants explicitly to introspect on their own grouping perception, clear evidence for such a deficit remains elusive. To resolve this issue, we adopt an index of Gestalt grouping from the object‐based attention literature that does not require participants to assess their own grouping perception. Children with ASD and mental‐ and chronological‐age matched typically developing children (TD) performed speeded orientation discriminations of two diagonal lines. The lines were superimposed on circles that were either grouped together or segmented on the basis of color, proximity or these two dimensions in competition. The magnitude of performance benefits evident for grouped circles, relative to ungrouped circles, provided an index of grouping under various conditions. Children with ASD showed comparable grouping by proximity to the TD group, but reduced grouping by similarity. ASD seems characterized by a selective bias away from grouping by similarity combined with typical levels of grouping by proximity, rather than by a pervasive integration deficit.

Between-object binding and visual attention

Many previous studies have found that we can attend pairs of visual features (e.g., colour, orientation) more efficiently when they belong to the same “object” compared to when they belong to separate, neighbouring objects (e.g., Behrmann, Zemel, & Mozer, 1998; Egly, Rafal, & Driver, 1994). This advantage for attending features from the same object may reflect stronger binding between these features than arises for pairs of features belonging to separate objects. However, recent findings described by Davis, Welch, Holmes, and Shepherd (in press) suggest that under specific conditions this same-object advantage can be reversed, such that attention now spreads more readily between features belonging to separate neighbouring objects than between features of the same object. In such cases it would appear that features belonging to separate visual objects are more strongly bound than features of the same object. Here I review these findings and present the results of a new study. Together these data suggest that magnocellular processes in the human visual system bind together features from separate objects, whereas parvocellular processes bind together features from the same object.