Biomedical subjects

Scott Glover

Publications and source records attributed to Scott Glover.

4 recordsLinked to original sources

PubMed2003

Modeling the time-dependent effect of the Ebbinghaus illusion on grasping.

Various authors have reported a small but consistent effect of the Ebbinghaus illusion on the maximum opening of the hand during prehension. This effect has been interpreted in various ways. In the present study, we focus on the time-course of the effect of contextual elements on grasping. The analysis presented here is based on a model for the control of the digits that uses two movement parameters (the approach parameter and the intended contact positions). These two parameters are based on different spatial attributes (flanker-target distance and target-edge position). As we assume that the perception of both attributes is veridical, there is no need for on-line corrections in the model. We show that this model predicts all time-dependent effects of the Ebbinghaus display on grasping. Human behavior can show a reduction in context effects over time without assuming an underlying shift from illusory towards veridical size information.

Hand Strength↗

PubMed2002

Semantics affect the planning but not control of grasping.

The semantic meaning of a word label printed on an object can have significant effects on the kinematics of reaching and grasping movements directed towards that object. Here, we examined how the semantics of word labels might differentially affect the planning and control stages of grasping. Subjects were presented with objects on which were printed either the word "LARGE" or "SMALL." When the grip aperture in the two conditions was compared, an effect of the words was found early in the reach, but this effect declined continuously as the hand approached the target. This continuously decreasing effect is consistent with a planning/control model of action, in which cognitive and perceptual variables affect how actions are planned but not how they are monitored and controlled on-line. The functional and neurological bases of semantic effects on planning and control are discussed.

Hand Strength↗

PubMed2002

Visual illusions affect planning but not control.

Much debate has arisen over how to account for the pattern of effects of visual illusions on action - that is, the findings that illusions affect actions in some circumstances but not others. I propose that this pattern can best be explained by postulating that visual illusions affect the planning of actions but do not affect the on-line control of actions. Strong evidence for this viewpoint comes from recent studies that show 'dynamic illusion effects': a large illusion effect early in a movement, but a decreasing effect as the hand approaches the target. These findings pose difficulties for other models of illusion effects on action.

Journal Article↗

PubMed2002

Dynamic effects of the Ebbinghaus illusion in grasping: support for a planning/control model of action.

A distinction between planning and control can be used to explain the effects of context-induced illusions on actions. The present study tested the effects of the Ebbinghaus illusion on the planning and control of the grip aperture in grasping a disk. In two experiments, the illusion had an effect on grip aperture that decreased as the hand approached the target, whether or not visual feedback was available. These results are taken as evidence in favor of a planning/control model, in which planning is susceptible to context-induced illusions, whereas control is not. It is argued that many dissociations between perception and action may better be explained as dissociations between perception and on-line control.

Attention↗