Importance of relative width differences and instructions on shape constancy performance

Adult subjects were instructed to select either the wider physical or the wider perspective shape of two rotated rectangles. With equal differences between the physical and perspective widths, responses were governed by instructions and by the magnitude of the differences between widths of the forms. However, with unequal differences between physical and perspective widths of the two rectangles, responses were governed primarily by the magnitude of the differences. Regardless of instructions, responses were to the dimension with the greater difference between widths. The results suggest that performance in the shape constancy experiment is a function of relative dimensional discriminability, as defined by instructions, and relative differences of widths between forms presented for comparison.     

A demonstration of shape constancy

In order to compare the recognition of objective (defined in three dimensions) and projective (on the frontal-parallel plane) shapes, subjects were asked to identify angles (either objective or projective) on random polygons that were displayed in complex and meaningful photographic slides in the frontal-parallel plane. The subjects’ judgments corresponded much more closely to the objective than to the projective shapes, almost independently of which of the two shapes they were asked to judge and of whether the slides were presented in a normal upright orientation or were rotated 180 deg. The results are incompatible with the strong form of the shape-slant hypothesis, which assumes that the primary perceptual information concerns the properties of the projective retinal image. The results indicate, instead, that a tacit conception of three-dimensional space is primary in the perceptual process.     

Projective invariance and visual shape constancy

As one moves about a table, the projection of its shape on the retina varies enormously, yet the table's shape appears constant. The various retinal images of a single object are nearly congruent in projective geometry. To explain apparent constancy, standard theories of vision assume that the visual system has access to this projective congruence. We present four experiments that undermine this assumption (i.e., the projective thesis). The basic result is that observers' estimates of shape in a simple production task represent gross departures from correct projection, even when observers are given aids to fixation. We manipulate both observer sample and experimental procedure in an attempt to find a source of these persistent errors. Our present hypothesis is that observers lack the sensitivity or implicit knowledge of projective geometry that has been attributed to them.     

The influence of object size and surface shape on shape constancy from stereo

The failure of shape constancy from stereoscopic information is widely reported in the literature. In this study we investigate how shape constancy is influenced by the size of the object and by the shape of the object's surface. Participants performed a shape-judgment task on objects of five sizes with three different surface shapes. The shapes used were: a frontoparallel rectangle, a triangular ridge surface, and a cylindrical surface, all of which contained the same maximum depth information, but different variations in depth across the surface. The results showed that, generally, small objects appear stretched and large objects appear squashed along the depth dimension. We also found a larger variance in shape judgments for rectangular stimuli than for cylindrical and ridge-shaped stimuli, suggesting that, when performing shape judgments with cylindrical and ridge-shaped stimuli, observers rely on a higher-order shape representation.     

Effects of form rotation on the speed of classification: the development of shape constancy

Ss classified a test form as matching or not matching one of a set of memorized forms relative to which the test forms were rotated up to 90 deg. “Match” reaction times increased monotonically with both number of forms memorized and degrees of rotation. Disappearance of the rotation effect after practice was attributed to a change from considering rotational information during comparison to comparing rotation invariant features. The change in strategy is considered an indicant of the development of shape constancy. Time taken to memorize the patterns increased linearly with the size of the memory set, justifying interpretation of the RT effects in terms of comparison time differences rather than differences in memorial specification of the patterns.     

Fine orientation discrimination and shape constancy in young infants

The present study aimed to investigate simultaneously fine orientation discrimination and shape constancy in young infants. The design employed two variants of the habituation paradigm. Infants in one group were habituated to a single orientation (5 or 15 degrees) of a single stimulus presented repeatedly, and they were then tested with the complementary orientation (15 or 5 degrees). Infants in a second group were habituated to several orientations (5, 10, and 15 degrees) of the same stimulus, and they were then tested with a familiar orientation of the stimulus, with two novel orientations of the same stimulus, and with a new stimulus. Between-groups comparison showed that infants habituated more efficiently to re-presentations of a single orientation than to multiple orientations of the same stimulus, providing evidence of fine orientation discrimination; posthabituation comparison within the single-orientation group confirmed that infants discriminated small orientation changes. Posthabituation comparison within the multiple-orientation group showed that infants generalized over novel orientation changes of the familiar stimulus though they discriminated change to a novel stimulus. Cumulatively, the results of this study demonstrate that under one set of conditions young infants show sensitivity to relatively fine variations in pattern orientation, but that under a different set of conditions young infants give evidence of shape constancy with the same patterns.     

Following navigation instructions presented verbally or spatially: Effects on training,retention and transfer

Two experiments investigated participants' ability to follow navigation instructions in a situation simulating communication between air traffic controllers and aircrews. A verbal condition, in which instructions were given orally, was compared with a spatial condition, in which commands were shown on a computer display as simulated movements, with the presentation times in the two conditions equated. Retention and transfer were studied a week later when participants performed in either the same or the other condition. In both sessions, participants' initial proportion correct was much higher in the spatial than in the verbal condition, but after three blocks, accuracy in the two conditions was equivalent. Retention was perfect when training and test conditions matched. Training in the verbal condition transferred to the spatial condition but not vice versa. Thus, there is evidence that participants' representations of the movements in the verbal and spatial conditions were not equivalent. Published in 2009 by John Wiley & Sons, Ltd.     

Judging the cross on rings: a matter of achieving shape constancy

The present study examines the influence of viewing position, experience, processing time, and attention on shape constancy in gymnastics judging. In an experiment, 40 gymnastics judges and as many laypeople were presented with a series of photographs that show athletes holding a ‘cross on rings’. They were simultaneously taken from different viewpoints. Participants had to judge how many degrees the arms deviated from horizontal for each picture. One half of the participants had a secondary task, to judge the duration of the picture presentation, which varied also. The overall performances of the gymnastics judges were much better than those of the laypeople, and in contrast to the lay‐judgments, they were not influenced by the secondary task. However, gymnastics judges were still significantly influenced by viewpoint, that is, their error rate increased with an increase in deviation from a frontal view. Copyright © 2005 John Wiley & Sons, Ltd.     

Effects of attentional-focus instructions on movement kinematics

BackgroundRecent research has shown that internal (body-related) attention-focus instructions disrupt motor learning and performance, whereas paying attention to the environmental effects of movements (external focus) leads to better performance than an internal focus [see, for reviews, Wulf, G. (2007). Attentional focus and motor learning: a review of 10 years of research. E-Journal Bewegung und Training, 1, 4–14.; Wulf, G., &; Prinz, W. (2001). Directing attention to movement effects enhances learning: a review. Psychonomic Bulletin &; Review, 8, 648–660.]. However, Beilock's studies [Beilock, S. L., Bertenthal, B. I., McCoy, A. M., &; Carr, T. H. (2004). Haste does not always make waste: expertise, direction of attention, and speed versus accuracy in performing sensorimotor skills. Psychonomic Bulletin &; Review, 11, 373–379.] suggest that an internal focus is detrimental in experts but not in novices. Because detrimental effects of consciously attending to movements have generally been measured by performance scores such as accuracy scores or reaction times, it remains unclear how internal and external attentional-focus instructions influence movement kinematics when learning a new skill. To fill this gap, the present study investigated attentional-focus effects on a biomechanical level.MethodsA video of an expert juggler demonstrating a two-ball juggling task was presented to juggling novices. Experimental groups were given either body-related (internal group) or ball-related (external group) verbal instructions or no attention-guiding instructions (control group). In the retention phase without attention-guiding instructions, the body-movement and ball-flight aspects of performance focused on in the verbal instruction were subjected to biomechanical analyses.Results and ConclusionsJuggling performance improved equally in all three groups. However, internally vs. externally instructed acquisition phases had differential effects on the kinematics of the upper body as well as ball trajectories when performing the juggling task. Remarkably, ball trajectories in the control group who received no specific attentional cueing were similar to those in the externally instructed group. This suggests that task-relevant information is picked up independently of instructions, and that external instructions provide redundant information. Internal instructions for object-related tasks, however, may confront novice learners with the need to process additional information. As a result, task difficulty might be unnecessarily enhanced in an observational learning setting.     

Effects of instructions and format on reported visual imagery

156 subjects (students and working adults) completed Marks' Vividness of Visual Imagery Questionnaire in one of two formats reflecting item order (blocked, random) under one of three instructional conditions (easy, neutral, difficult) reflecting ease of image formation. Although the effect of instructions (but not format) was significant, scores were lower, i.e., more vivid imagery was reported, in the easy than in the neutral or difficult conditions, which did not differ. These results suggest that the validity of Marks' questionnaire is not seriously weakened by response leniency.