Biomedical subjects

Rebecca Lawson

Publications and source records attributed to Rebecca Lawson.

8 recordsLinked to original sources

PubMed2006

Errors in judging information about reflections in mirrors.

We investigated people's perception and knowledge of planar mirror reflections. People were accurate at deciding when they could first see their reflection as they approached a mirror from the side, but only if their reflection was visible. Most people stopped too early if the mirror was covered up. People also overestimated the size of the reflection of their face on the surface of a mirror if they were shown a covered mirror. Their accuracy improved somewhat if their reflection was visible but, unlike the first task, they still made striking errors. Perceptual feedback thus improved performance at predicting the behaviour of mirror reflections in both tasks but failed to eliminate errors in the second task. The overestimation of reflection size was not face-specific as it generalised to novel stimuli (paper ellipses) and it was found with both a matching response and for verbal size estimations. The early error in the first task appears to be due to an inaccurate belief that can be overridden by perceptual feedback. The overestimation in the second task is primarily caused by a powerful size-constancy effect.

Adolescent↗

PubMed2006

Visual search for a circular region perceived as a figure versus as a hole: evidence of the importance of part structure.

To study contour curvature polarity, we compared strictly convex regions (circular figures) with strictly concave regions (circular holes). We tested for an asymmetry between visual searches for concavities and those for convexities. We found that providing a preview of the background benefited search for concavities (holes) more than it did search for convexities (figures) and that for convex figures, nearer targets were responded to more quickly. Importantly, however, we failed to find any support for the hypothesis that concave targets are inherently more salient. We conclude that previous findings in the literature, which have been taken to indicate preferential processing of concavities, due to their increased salience, are more likely the result of an early computation of part structure based on concavities.

Depth Perception↗

PubMed2006

Comparing view sensitivity in shape discrimination with shape sensitivity in view discrimination.

In three picture-picture matching experiments, the effects of a view change on our ability to detect a shape change (Experiments 1 and 2) were contrasted with the effects of a shape change on our ability to detect a view change (Experiment 3). In each experiment, both view changes and shape changes influenced performance. However, shape changes had more influence than did view changes in the shape change detection task Conversely, view changes were more influential when the task was to detect view changes. Thus, the participants could often discriminate between the effects of shape changes and the effects of view changes. The disruptive effect of task-irrelevant changes (view changes in the first two experiments; shape changes in the final experiment) does not support Stankiewicz's (2002) claim that information about viewpoint and about shape can be estimated independently by human observers. However, the greater effect of variation in the task-relevant than in the task-irrelevant dimension indicates that the observers were moderately successful at disregarding irrelevant changes.

Attention↗

PubMed2004

Recognizing a plane-misoriented view of a familiar object is not influenced by the ease of specifying the main axis of elongation of that object.

Participants saw three versions of pictures of familiar objects: the original unaltered (axis-normal) pictures, axis-extended pictures in which the main axes of the axis-normal pictures were elongated, and axis-switched pictures in which objects that were originally horizontally elongated were depicted as vertically elongated and vice versa. Relative to axis-normal pictures, axis extension aided decisions about whether the picture of the object was wide or tall, and axis switching hindered these decisions for both upright and plane-misoriented views. Nevertheless, although these axis manipulations clearly influenced decisions about the location of the object's main axis of elongation, axis-switched pictures were no harder to name than axis-extended pictures. Changing the depicted main axis of elongation by axis switching and axis extension did not influence object recognition in itself, whether for upright or for plane-misoriented views. This suggests that specifying the main axis of elongation of an object does not play an important role in the orientation-sensitive processes involved in identifying plane-misoriented views of that object.

Form Perception↗

PubMed2004

View sensitivity increases for same-shape matches if mismatches show pairs of more similar shapes.

Lawson, Bülthoff, and Dumbell (2003) found increased view sensitivity when more similar shapes had to be discriminated. Their sequential picture-picture matching studies showed depth-rotated views of novel, complex, 3-D objects. However, with a similar task and stimuli, Hayward and Williams (2000) found no variation in view sensitivity on same-shape match trials depending on whether similar or dissimilar pairs of shapes were shown on mismatch trials. Thus view sensitivity increases from dissimilar-shape mismatches to similar-shape mismatches to same-shape matches (Lawson et al., 2003). However, view sensitivity may not increase on same-shape matches if those trials are combined with similar-rather than dissimilar-shape mismatches (Hayward & Williams, 2000). The latter result was reexamined here. Matches were view sensitive given even the dissimilar-shape mismatch context. This view sensitivity increased in the medium and especially the hard contexts that showed similar shapes on mismatches. Thus, indirectly increasing shape similarity via mismatch context modulated view-change effects (cf. Hayward & Williams, 2000).

Discrimination, Psychological↗

PubMed2004

Depth rotation and mirror-image reflection reduce affective preference as well as recognition memory for pictures of novel objects.

In two experiments, the identification of novel 3-D objects was worse for depth-rotated and mirror-reflected views, compared with the study view in an implicit affective preference memory task, as well as in an explicit recognition memory task. In Experiment 1, recognition was worse and preference was lower when depth-rotated views of an object were paired with an unstudied object relative to trials when the study view of that object was shown. There was a similar trend for mirror-reflected views. In Experiment 2, the study view of an object was both recognized and preferred above chance when it was paired with either depth-rotated or mirror-reflected views of that object. These results suggest that view-sensitive representations of objects mediate performance in implicit, as well as explicit, memory tasks. The findings do not support the claim that separate episodic and structural description representations underlie performance in implicit and explicit memory tasks, respectively.

Affect↗

PubMed2003

Recognition thresholds for plane-rotated pictures of familiar objects.

We investigated picture plane rotation effects on the minimum stimulus duration required to recognise pictures of familiar objects in a picture-word verification task. Participants made unspeeded responses, selecting from 126 written alternatives. Longer stimulus durations were needed to identify plane-misoriented views. These orientation effects were non-linear, arguing against a simple mental rotation account of compensation for plane misorientation in identification tasks. Orientation effects were found for almost all items, in particular including those labelled at the basic level (cf. Hamm, McMullen, 1998, Journal of Experimental Psychology: Human Perception and Performance 24, 413-426). We suggest that plane misorientation increases the difficulty of basic level as well as subordinate level identification unless only a small, visually dissimilar set of stimuli are presented. Errors in the task were analysed to provide an alternative, objective measure of perceived visual similarity, by assessing the number and nature of mistaken identifications made to a given target object. We propose that misorientation effects are best understood in terms of the effects of the perceived visual similarity of a target to its set of response alternatives rather than in terms of the level (basic or subordinate) at which the target is to be identified.

Humans↗

PubMed2003

Interactions between view changes and shape changes in picture-picture matching.

Four experiments are reported in which pictures of different morphs of novel, complex, 3-D objects, similar to objects which we must identify in the real world, were presented. We investigated how changes of viewpoint influence our ability to discriminate between morphs. View changes had a powerful effect on performance in picture-picture matching tasks when similarly shaped morphs had to be discriminated. Shape changes were detected faster and more accurately when morphs were depicted from the same rather than different views. In contrast, view change had no effect when dissimilarly shaped morphs had to be discriminated. This interaction between the effects of view change and shape change was found both for simultaneous stimulus presentation and for sequential presentation with interstimulus intervals up to 3600 ms. The interaction was found after repeated presentations of the stimuli before the matching task and after practice at the matching task as well as after no such pre-exposure to the stimuli or to the task. The results demonstrate the difficulty in activating abstract, view-insensitive representations to help to achieve object constancy, even when matching over long interstimulus intervals or after stimuli have already been seen many times.

Adult↗