Foreground and background in dynamic spatial orientation

The dependency of visually induced self-motion sensation upon the density of moving contrasts as well as upon additional stationary contrasts in the foreground or background was investigated. Using two different optokinetic stimuli, a disk rotating in the frontoparallel plane, and the projection of horizontally moving stripes onto a cylindrical screen, it was found that: (1) visually induced self-motion depends upon the density of moving contrasts randomly distributed within the visual field and, with a single contrast area of 1/4 %, is saturated when about 30% of the visual field is moving; (2) additional stationary contrasts inhibit visually induced serf-motion, proportional to their density; and (3) the location in depth of the stationary contrasts has a significant effect upon this inhibition. Their effect is considerable when located in the background of the moving stimuli but weak when appearing in the foreground. It is concluded that dynamic visual spatial orientation relies mainly on information from the seen periphery, both retinal and depth.     

Active control in interrupted dynamic spatial orientation: The detection of orientation change

Gibson (1966, 1979) suggested that an important property of perception is that the observer is active. Two experiments were conducted to examine the benefits of active observation in determining dynamic spatial orientation. Subjects were presented with displays simulating locomotion through a three-dimensional environment. Active observers continuously controlled locomotion, whereas passive observers viewed the display. During the trial, the display was blacked out for a brief period, followed by a static image that was at either the correct or the incorrect orientation following the blackout. Subjects were required to indicate whether they were positioned at the correct extrapolated orientation. The presence or absence of orientation change, the type of change (changes in rotation about the depth axis [roll], horizontal axis [pitch], or forward translation), the duration of the blackout, and the consistency of change were varied. In addition, the experiments used either a compensatory or a pursuit tracking task. Active observers had greater sensitivity than did passive observers in detecting a change for both tracking tasks. Subjects in both experiments exhibited greater sensitivity in detecting inconsistent changes (relative to consistent changes), suggesting that the dynamics specified by optical flow were incorporated in extrapolated orientation. In addition, sensitivity decreased with an increase in blackout duration. The results are discussed in terms of an extrapolation model of perception that incorporates the responses executed by active observers.     

Illusory contours and spatial judgment

We investigated whether, in the human visual system, the mechanisms responsible for relative location judgments are the same when those judgments are made in the context of illusory contours and in the context of mentally joining two points. We asked subjects to align a dot with the oblique contour of an illusory surface or to align a dot with two markers at an oblique orientation. The systematic errors differed in direction for these two conditions. All the systematic errors were orientation dependent. The errors in aligning a dot with an illusory contour seem to be related to the asymmetrical shape of the single objects, which are able to induce an illusory contour, as well as figure-ground segregation.     

Effects of peripheral eccentricity and head orientation on gaze discrimination

Visual search tasks support a special role for direct gaze in human cognition, while classic gaze judgement tasks suggest the congruency between head orientation and gaze direction plays a central role in gaze perception. Moreover, whether gaze direction can be accurately discriminated in the periphery using covert attention is unknown. In the present study, individual faces in frontal and in deviated head orientations with a direct or an averted gaze were flashed for 150 ms across the visual field; participants focused on a centred fixation while judging the gaze direction. Gaze discrimination speed and accuracy varied with head orientation and eccentricity. The limit of accurate gaze discrimination was less than ±6° eccentricity. Response times suggested a processing facilitation for direct gaze in fovea, irrespective of head orientation, however, by ±3° eccentricity, head orientation started biasing gaze judgements, and this bias increased with eccentricity. Results also suggested a special processing of frontal heads with direct gaze in central vision, rather than a general congruency effect between eye and head cues. Thus, while both head and eye cues contribute to gaze discrimination, their role differs with eccentricity.     

The independence of dynamic spatial orientation from luminance and refractive error

The effect of refractive error and luminance on circularvection, the illusory sensation of self-motion resulting from rotation of the visual field, was determined. Neither reduction of luminance to levels near absolute scotopic threshold nor induced refractive errors of more than 16 diopters abolished circularvection or influenced any of its latency measures. The results are discussed in terms of the role of the peripheral visual field and the nature of the visual stimulus in ego orientation.     

Pattern alternation: Effects of spatial frequency and orientation

Campbell and Howell (1972) reported an effect called “monocular pattern alternation.” They found that a pattern composed of two orthogonal sinusoidal gratings, one horizontal and the other vertical, underwent rivalry when viewed monocularly for a period of time. In the present study, it has been shown that monocular pattern alternation depends upon the orientation of the pattern and the spatial frequency of its components. Fewer reversals were found for an obliquely oriented pattern than for a pattern with components in the horizontal and vertical meridians. Alternation rate was higher when the gratings were similar in frequency but differed in orientation than when the components of the pattern differed in both dimensions. It was concluded that pattern alternation reflects an antagonistic interaction between interdependent channels in the human visual system that respond to orientation and spatial frequency.     

Occlusion cues contribute to orientation judgments of occlusion-defined contours

Occlusion cues defining a contour in a 2-D stimulus pattern were shown to contribute to the accuracy of orientation judgments of that contour. The stimulus pattern was altered so that the occlusion cues became ambiguous, by introducing a textured background suggesting transparency of the stimulus pattern. Orientation judgments then became significantly less accurate. This finding shows that occlusion cues in 2-D patterns can be behaviorally relevant, in addition to generating the subjective percept commonly known as an illusory contour. The disruptive effect of the textured background on orientation judgments remained when no texture elements were present in the vicinity of the contour. This suggests that the generation of occlusion-defined contours relies as much on an evaluation of the surfaces at either side of the contour as being opaque as it does on local encoding of occlusion cues close to the contour. Finally, orientation sensitivity measured with contours defined by other than occlusion cues was not altered after the introduction of a textured background.     

Hue difference contours can be used in processing orientation information

In most studies of orientation processing, chromatic information and achromatic information have been combined or confounded. The present experiments investigated the relative sizes of tilt aftereffect induced by these two types of information. In these experiments, the tilt aftereffect is the error in adjusting a test contour to vertical, following the scanning of an inspection contour. For inspection and test contours identical except for orientation, the tilt aftereffects varied with inspection contour orientation but not with chromatic or achromatic condition. Smaller tilt aftereffects were obtained when the inspection contour was produced by a hue difference (chromatic information) and the test contour was produced by a luminance difference (achromatic information), or vice versa. These results indicate that achromatic and chromatic information is processed in a similar manner with respect to orientation. Furthermore, there is substantial, but incomplete, pooling of chromatic and achromatic orientation information.     

Effects of genetic vestibular defects on behavior related to spatial orientation and emotionality.

A large battery of behavioral tests was administered to normal mice and to mice with varying degrees of otoconial agenesis due to genes affecting vestibular development. Many significant differences were found, but a factor analysis revealed that the variance on the 11 best tests could be accounted for in terms of two underlying variables. Factor I, the more important of the two, was associated with activity, habituation, and spontaneous alternation. Factor II appeared to represent a fear of new stimuli or situations. In both cases factor scores were highly related to the degree of otoconial deficiency. One subgroup of mice with severe otoconial agenesis displayed hyperactivity and a total absence of either habituation or spontaneous alternation. In these animals, brain and body development were stunted, and the reactions to amphetamine and physostigmine were opposite to those seen in normal mice. The results support the idea that the static organs contribute importantly to spatial orientation and suggest that early-onset vestibular defects can result in profound alterations of emotionality.     

Effects of flicker-induced depth on chromatic subjective contours

Two experiments examined the dependence of illusory colors on boundary salience and depth stratification by using flicker-induced depth. The first used a subjective-contour stimulus that appeared as a translucent colored rectangle covering a set of inducing circles and a dark background. The circles were then flickered so as to be perceived as background, and the previously dark background moved forward and appeared as foreground. Simultaneously, the chromatic subjective contour was eliminated. In the second experiment, a subjective-contour (faces/vase-concentric squares) figure was tinted with the McCollough effect, which produced a strong subjective color edge. This edge was visible only with the faces/vase percept and not in the squares percept. Flickering the target locked it into the square configuration because in this case the flicker held the entire pattern in the same depth plane. This eliminated the subjective color edge. Depth stratification and subjective color blockage were maximal at a flicker rate of 6 Hz.     

Effects of left-right orientation and position reversals on spatial perspective taking in young children.

50 boys and 50 girls, from Grades K through 4, were presented with 180 degrees perspective-taking tasks that varied arrays in terms of the number of front-back and left-right orientation reversals and left-right position reversals. Results confirmed existing evidence that left-right orientation reversals are more difficult than front-back orientation reversals in arrays of one object. However, with arrays of two objects, left-right orientation reversals appear easier than front-back orientation reversals, apparently because of the relationship between the objects.     

Sexual orientation and spatial memory

The present study aimed at determining the influence of sexual orientation in human spatial learning and memory. Participants performed the Boxes Room, a virtual reality version of the Holeboard. In Experiment I, a reference memory task, the position of the hidden rewards remained constant during the whole experiment. In Experiment II, a working memory task, the position of rewards changed between blocks. Each block consisted of two trials: One trial for acquisition and another for retrieval. The results of Experiment I showed that heterosexual men performed better than homosexual men and heterosexual women. They found the rewarded boxes faster. Moreover, homosexual participants committed more errors than heterosexuals. Experiment II showed that working memory abilities are the same in groups of different sexual orientation. These results suggest that sexual orientation is related to spatial navigation abilities, but mostly in men, and limited to reference memory, which depends more on the function of the hippocampal system.     

A Stroop effect for spatial orientation

The author investigated the conditions under which a congruent or incongruent orientation word affects processing of the orientation of visual objects. Participants named the orientation of a rectangle that partially occluded another rectangle. Congruent or incongruent orientation words appeared in the relevant object, in the irrelevant object, or in the background. There were two main results. First, congruent orientation words produced faster orientation-naming responses than incongruent orientation words. This finding constituted a new Stroop effect for spatial orientation. Second, only words in the relevant (i.e., attended) object produced Stroop effects, whereas words outside the relevant object had no significant effects. This object-dependent modulation of Stroop effects resembled previous findings with color-naming tasks, and hence indicated that these modulations are not restricted to a particular type of task. In summary, results suggested that object-based attention plays an important role in processing of irrelevant words.     

An analysis of spatial orientation test performance

Spatial Orientation ability correlates with important criteria such as achievement in calculus and physics, but this ability has not been investigated systematically. Performance on individual items adapted from a standard test of Spatial Orientation was studied. Subjects judged whether aerial views would be seen by an observer oriented in various ways. For practiced subjects, the time to answer items was an approximately linear function of the number of abstract spatial dimensions on which the aerial view and the observer's orientation were consistent. Practice led to lower error rates and lower intercepts for the response-time functions. Subject's ability correlated with the linearity of their response-time functions suggesting that lower ability subjects fail to code one or more spatial dimensions. A model specifying serial, self-terminating comparison of abstract spatial dimensions is proposed as an ideal which subjects approach after practice.