Biomedical subjects

I M Thornton

Publications and source records attributed to I M Thornton.

3 recordsLinked to original sources

PubMed2001

Attention-based visual routines: sprites.

A central role of visual attention is to generate object descriptions that are not available from early vision. Simple examples are counting elements in a display or deciding whether a dot is inside or outside a closed contour (Ullman, Cognition 18 (1984) 97). We are interested in the high-level descriptions of dynamic patterns - the motions that characterize familiar objects undergoing stereotypical action - such as a pencil bouncing on a table top, a butterfly in flight, or a closing door. We examine whether the perception of these action patterns is mediated by attention as a high-level animation or 'sprite'. We have studied the discrimination of displays made up of simple, rigidly linked sets of points in motion: either pairs of points in orbiting motion or 11 points in biological motion mimicking human walking. We find that discrimination of even the simplest dynamic patterns demands attention.

Attention↗

PubMed2001

Exploring the link between time to collision and representational momentum.

Previous research has shown that when a moving object is occluded prior to collision with another stationary object, observers tend to consistently underestimate the physical/actual time to collision (TTC). We examined whether mislocalization of the initial point of disappearance plays any role in this underestimation. To assess the contribution of mislocalization, we coupled a standard TTC paradigm with a representational-momentum paradigm. Representational momentum refers to the tendency to mislocalize the remembered stopping point of a moving object as being too far forward along an actual or implied path of motion. Using identical displays we found large representational-momentum shifts and consistent underestimation of TTC. When the displays were modified to disambiguate the point of disappearance, representational momentum was absent or significantly reduced and underestimates of TTC were effectively eliminated. These results strongly suggest that the represented point of disappearance is an important factor in TTC estimation and that systematic forward displacement of this point may partially explain frequently observed underestimation.

Cues↗

PubMed2000

An implicit measure of undetected change.

Several paradigms (e.g. change blindness, inattentional blindness, transsaccadic integration) indicate that observers are often very poor at reporting changes to their visual environment. Such evidence has been used to suggest that the spatio-temporal coherence needed to represent change can only occur in the presence of focused attention. However, those studies almost always rely on explicit reports. It remains a possibility that the visual system can implicitly detect change, but that in the absence of focused attention, the change does not reach awareness and consequently is not reported. To test this possibility, we used a simple change detection paradigm coupled with a speeded orientation discrimination task. Even when observers reported being unaware of a change in an item's orientation, its final orientation effectively biased their response in the orientation discrimination task. Both in aware and unaware trials, errors were most frequent when the changed item and the probe had incongruent orientations. These results demonstrate that the nature of the change can be represented in the absence of awareness.

Awareness↗