scholarly journals Orientational Effects and Component Processes in Symmetry Detection

1992 ◽  
Vol 44 (3) ◽  
pp. 475-508 ◽  
Author(s):  
Johan Wagemans ◽  
Luc Van Gool ◽  
Géry d'Ydewalle
Keyword(s):  
Randomized Trial ◽  
Significant Interaction ◽  
Bilateral Symmetry ◽  
Symmetry Detection ◽  
Orientation Experiment ◽  
Component Processes ◽  
Axis Of Symmetry ◽  
Random Dot Patterns

In previous research on symmetry detection, factors contributing to orientational effects (axis and virtual lines connecting symmetrically positioned dots) and component processes (axis selection and pointwise evaluation) have always been confounded. The reason is the restriction to bilateral symmetry (BS), with pointwise correspondences being orthogonal to the axis of symmetry. In our experiments, subjects had to discriminate random dot patterns from symmetries defined by combining 12 axis orientations (every 15°) with seven reflection angles (0°, yielding BS, and three clockwise and counterclockwise 15° steps, yielding skewed symmetry, SS). In Experiment 1, with completely randomized trial order, a significant interaction between axis and skewing angle was obtained, indicating that classically observed orientational effects are restricted to BS and that the orientation of the pointwise correspondences is important. These basic findings were replicated in three subsequent experiments, which differed in that they used blocks containing patterns with the same axis (Experiment 2), virtual lines orientation (Experiment 3), or their combination (Experiment 4). Based on a comparison between the results obtained by these manipulations, we suggest a possible reason for the failure of preattentive symmetry detection in the case of dot patterns with SS.

scholarly journals Aging and Bilateral Symmetry Detection

2002 ◽  
Vol 57 (3) ◽  
pp. P241-P245 ◽  
Author(s):  
A. M. Herbert ◽  
O. Overbury ◽  
J. Singh ◽  
J. Faubert
Keyword(s):  
Bilateral Symmetry ◽  
Symmetry Detection

The Differential Effects of Simultaneous and Successive Cueing on the Detection of Bilateral Symmetry in Dot Patterns

2000 ◽  
Vol 53 (1) ◽  
pp. 165-190 ◽  
Author(s):  
Peter Wenderoth
Keyword(s):  
Visual Processing ◽  
Processing Time ◽  
Reaction Times ◽  
Vertical Axis ◽  
Bilateral Symmetry ◽  
Frame Of Reference ◽  
Symmetry Detection ◽  
Axis Orientation ◽  
Differential Effects ◽  
Orientation Ordering

Corballis and Roldan (1975) obtained speeded judgements of whether dot patterns were bilaterally symmetrical about, or translated across, a line. Reaction times (RTs) were ordered V (vertical) > D (diagonal) > H (horizontal) where “>” means faster than. Similar results occurred with blocked axis orientations, suggesting subjects cannot prepare by rotating a mental frame of reference. Blocking trials may have been ineffective because blocking cannot provide incremental benefits over those already provided by axis lines. Four experiments show that the usual axis orientation ordering of V > H > D is markedly attentuated by simultaneous but not successive axis lines. Also, axis cue lines and axis blocking are not equivalent treatments. Instead, unblocked line cues require finite processing time whereas, under blocking, subjects can prepare for the expected orientation. There was no suggestion anywhere of the V > D > H axis ordering that Corballis and Roldan reported. Successive axis line cues may only direct attention to the orientation being cued, but simultaneous line cues may change the stimulus itself, thus providing an additional means of visual processing that facilitates symmetry detection at non-vertical axis orientations.

The Effects on Bilateral-Symmetry Detection of Multiple Symmetry, near Symmetry, and Axis Orientation

Perception ◽  
1997 ◽  
Vol 26 (7) ◽  
pp. 891-904 ◽  
Author(s):  
Peter Wenderoth
Keyword(s):  
Response Bias ◽  
Human Perception ◽  
Negative Stimulus ◽  
Bilateral Symmetry ◽  
Symmetry Detection ◽  
Axis Orientation ◽  
Second Stage ◽  
Asymmetrical Pattern ◽  
Stage Process ◽  
Axes Of Symmetry

Palmer and Hemenway (1978 Journal of Experimental Psychology: Human Perception and Performance4 691–702) reported that shapes with multiple axes of symmetry are processed faster than those with single symmetry even when trials are blocked so that the subject knows that any symmetry axis will be vertical. Because their model of symmetry detection postulated a two-stage process in which all orientations are searched crudely at first, in no particular order, followed by second-stage scrutiny, the continued salience of multiple over single symmetry with blocking could not be explained. They claimed that stimuli with multiple axes of symmetry have an additional ‘goodness’. Four experiments are reported in which it is demonstrated that both sensitivity ( d′) and response bias ( β) vary considerably in symmetry detection, not just as a function of the positive (symmetrical) stimuli used but also as a function of the negative or conjugate instances selected. Although stimuli with multiple axes of symmetry may well have extra salience due to pattern ‘goodness’, this factor may have been confounded with response bias in Palmer and Hemenway's experiments. It is suggested that several of their—as well as other researchers—results could be due to some combination of the effects of type of positive stimulus, type of negative stimulus, and response bias directed towards responding positively to highly symmetrical stimuli in a mix of less symmetrical stimuli. Palmer and Hemenway appear to have been correct in suggesting that subjects are more sensitive to quadruple than single symmetry, but the experiments indicate that subjects are also more willing to respond “symmetrical” to stimuli with quadruple symmetry when trials are not blocked, as in Palmer and Hemenway's experiment 1. However, it is demonstrated that the latter effect can be removed by blocking trials so that only one class of symmetrical pattern and one class of asymmetrical pattern occur in any block.

Perception of Self-Motion Induced by Moving-Dot Patterns: The Interaction of the Stimulating Area and the Speed of the Pattern

Perception ◽  
1997 ◽  
Vol 26 (1_suppl) ◽  
pp. 201-201
Author(s):  
C Kano
Keyword(s):  
Significant Interaction ◽  
Interactive Effects ◽  
Circular Area ◽  
Perception Of Self ◽  
Random Dot Patterns ◽  
Self Motion ◽  
Dark Room ◽  
Moving Pattern

A linear moving-dot pattern was presented to observers to induce self-motion. A stimulating circular area of more than 28.1 deg diameter induced self-motion perfectly, and even areas ranging from 5.7 deg to 11.4 deg diameter were able to elicit self-motion (Kano, 1995 Perception24 Supplement, 108). In the present study the interactive effects of the size of the stimulating area and the speed of the moving pattern on the perception of self-motion were examined. Random-dot patterns were moved downward in a circular area on a screen in a dark room. The diameters of the circular area were 5.7, 11.4, 22.6, and 43.6 deg. The speeds of the dot pattern were 9.49, 18.85, 28.07, 36.73, and 45.08 deg s−1. Observers were twenty-six students of Keio University. When the size of the area became larger and the dot pattern moved faster, self-motion was generally induced with shorter latencies. However, a significant interaction was found between size and speed; for the smallest area (5.7 deg diameter circle) latency was shorter at the lower speeds (9.49 to 28.07 deg s−1) than at the higher speeds (36.73 and 45.08 deg s −1). For the 11.4 deg diameter circle speed had no effect on latency. For the 22.6 deg diameter circle, however, latency decreased with increasing speed. For the 43.6 deg diameter circle latency was very short and constant under the four higher speeds, but remained considerably longer at the lowest speed. The results show that the effect of speed depends on the size of the stimulating area. When the size was large enough, speed had little effect on the latency of self-motion.

The Salience of Vertical Symmetry

Perception ◽  
1994 ◽  
Vol 23 (2) ◽  
pp. 221-236 ◽  
Author(s):  
Peter Wenderoth
Keyword(s):  
Additional Data ◽  
Oblique Effect ◽  
Axis Of Symmetry ◽  
Random Dot Patterns ◽  
Symmetry Perception ◽  
Axes Of Symmetry ◽  
Other Orientation ◽  
Relative Salience ◽  
Sensitivity Performance ◽  
Better Than

It has long been accepted that amongst patterns which are bilaterally symmetrical, those which have their axis of symmetry vertical are more saliently symmetrical than patterns whose axis of symmetry is at some other orientation. The evidence regarding the relative salience of other orientations of axis of symmetry is somewhat more equivocal. In experiment 1, subjects were required to discriminate between symmetric or random-dot patterns when the axis of symmetry was at one of eighteen different orientations, spaced 10° apart, both clockwise and counterclockwise of vertical to horizontal. The data indicated that vertical was most salient, then horizontal but that, unlike in the classical oblique effect for contrast sensitivity, performance for precisely diagonal axes was better than that for surrounding axis orientations. Additional data (from experiments 2 and 3) also showed that the salience of vertical and horizontal axes of symmetry can be manipulated extensively by varying the range of stimuli presented, presumably by manipulating the scanning or attentional strategy adopted by the observer. Many previous studies of symmetry perception may have confounded hard-wired salience for vertical symmetry with scanning or attentional strategies.

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