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D A Allport

Publications and source records attributed to D A Allport.

8 recordsLinked to original sources
PubMed1999

Hand-centred coding of target location in visuo-spatial working memory.

The aim of the present experiment was to determine the frame of reference used to encode a visually specified target location, in a simple, visuo-spatial short-term-memory task, using delayed manual pointing. Subjects were required to remember the location of a single, visually presented stimulus, over delays of 3 and 30 s, and to recall its location by pointing to it with the tip of a stylus with eyes closed. There were two starting positions for the hand: one near the body, proximal to the target area, the other far from the body, i.e., beyond the target area. Two groups of twelve subjects participated in the experiment. One group observed the target locations in the light, the other group observed the target LEDs in the dark. The results showed a large (between 10-30%) and consistent undershoot of the remembered target location with respect to the hand's starting position, in the sagittal axis, both when the hand started from the near and from the far position. That is, from the far starting position. pointing errors lay consistently beyond the actual target location as seen from the subject's viewpoint. Further, this undershoot error in the remembered target location increased over time delay. These results are in favour of the hypothesis that the visual target locations were encoded in a hand-centred frame of reference in spatial short-term memory. They also implicate the use of motor- or action-related representations in visuo-spatial working memory.

Adult↗
PubMed1997

Independent coding of target distance and direction in visuo-spatial working memory.

The organization of manual reaching movements suggests considerable independence in the initial programming with respect to the direction and the distance of the intended movement. It was hypothesized that short-term memory for a visually-presented location within reaching space, in the absence of other allocentric reference points, might also be represented in a motoric code, showing similar independence in the encoding of direction and distance. This hypothesis was tested in two experiments, using adult human subjects who were required to remember the location of a briefly presented luminous spot. Stimuli were presented in the dark, thus providing purely egocentric spatial information. After the specified delay, subjects were instructed to point to the remembered location. In Exp. 1, temporal decay of location memory was studied, over a range of 4-30 s. The results showed that (a) memory for both the direction and the distance of the visual target location declined over time, at about the same rate for both parameters; however, (b) errors of distance were much greater in the left than in the right hemispace, whereas direction errors showed no such effect; (c) the distance and direction errors were essentially uncorrelated, at all delays. These findings suggest independent representation of these two parameters in working memory. In Exp. 2 the subjects were required to remember the locations of two visual stimuli presented sequentially, one after the other. Only after both stimuli had been presented did the subject receive a signal from the experimenter as to which one was to be pointed to. The results showed that the encoding of a second location selectively interfered with memory for the direction but not for the distance of the to-be-remembered target location. As in Exp. 1, direction and distance errors were again uncorrelated. The results of both experiments indicate that memory for egocentrically-specified visual locations can encode the direction and distance of the target independently. Use of motor-related representation in spatial working memory is thus strongly suggested. The findings are discussed in the context of multiple representations of space in visuo-spatial short-term memory.

Adult↗
PubMed1989

Varieties of object constancy.

Three experiments are described in which two pictures of isolated man-made objects were presented in succession. The subjects' task was to decide, as rapidly as possible, whether the two pictured objects had the same name. With a stimulus-onset asynchrony (SOA) of above 200 msec two types of facilitation were observed: (1) the response latency was reduced if the pictures showed the same object, even though seen from different viewpoints (object benefit); (2) decision time was reduced further if the pictures showed the same object from the same angle of view (viewpoint benefit). These facilitation effects were not affected by projecting the pictures to different retinal locations. Significant benefits of both types were also obtained when the projected images differed in size. However, in these circumstances there was a small but significant performance decrement in matching two similar views of a single object, but not if the views were different. Conversely, the object benefit, but not the viewpoint benefit, was reduced when the SOA was only 100 msec. The data suggest the existence of (at least) two different visual codes, one non-retinotopic but viewer-centred, the other object-centred.

Adolescent↗
PubMed1978

Visualization of compound scenes.

Subjects listened to descriptions of familiar objects and the spatial relations between them and attempted to visualize these objects as a composite scene. The time taken to generate a composite visual image, measured from the end of the verbal description, increased dramatically and linearly with the number of objects in the scene. As this relationship was independent of the rate of presentation of the verbal description, over a wide range, it could not be due to the visualization process cumulatively lagging behind the verbal description. Our evidence indicates that this relationship is due to some process, necessary to the subjective visualization of a composite array as a whole, which commences only after the verbal description is complete.

Female↗