Visual space under free viewing conditions

Most research on visual space has been done under restricted viewing conditions and in reduced environments. In our experiments, observers performed an exocentric pointing task, a collinearity task, and a parallelity task in a entirely visible room. We varied the relative distances between the objects and the observer and the separation angle between the two objects. We were able to compare our data directly with data from experiments in an environment with less monocular depth information present. We expected that in a richer environment and under less restrictive viewing conditions, the settings would deviate less from the veridical settings. However, large systematic deviations from veridical settings were found for all three tasks. The structure of these deviations was task dependent, and the structure and the deviations themselves were comparable to those obtained under more restricted circumstances. Thus, the additional information was not used effectively by the observers.     

Distance perception under binocular and monocular viewing conditions

First, third, and fifth graders and college adults made judgments of absolute distance in a binocular (full-information) condition and in one of three monocular conditions: redundant texture gradient, compression gradient, and control (no texture). No age-related differences in accuracy of judgment were observed in any of the conditions. Substantial differences in the effectiveness of different kinds of information were found, however. The results indicate that the ability to register information for distance is well developed by first grade, but that substantial limitations exist on the visual system’s ability to process various forms of redundant information.     

Variations in apparent spatial frequency with stimulus orientation: IL Matching data collected under normal and interferometric viewing conditions

Using an adjustment procedure, human observers matched the apparent spatial frequencies of sinusoidal gratings presented in different orientations (0, 45, 90, and 135 deg). Matches were made between all possible pairwise orientation combinations. Significant match deviations indicated that the apparent frequency of a grating depends on its orientation. The most consistent deviations were found between horizontal and vertical gratings, with horizontal gratings appearing to be of a lower spatial frequency than vertical gratings. These effects were relatively independent of stimulus contrast and persisted when the optics of the eye were bypassed with laser interferometry. A neurophysiological explanation of these effects is proposed.     

Peripheral viewing and simultaneous contrast

An experiment was done to find the effect on simultaneous brightness contrast of viewing the test patches foveally or peripherally, at a distance of 3° or 6° from the fovea. It was found that contrast was greater in the periphery. It was also found that contrast increased with prolonged viewing of the display. A further experiment showed that blurring the test patches produced an increase in contrast.     

Size and distance judgments under reduced conditions of viewing

Magnitude estimations of the size and distance of a variable relative to a standard were obtained in the absence of distance cues. Estimates were provided by different groups under three conditions: (a) physical size and distance variant, visual angle of the variable constant and equal to the standard, (b) physical size constant, physical distance and visual angle of variable changing, and (c) physical distance constant, physical size and visual angle of the variable changing. The results in both experiments were very similar. In each case both size and distance estimates conformed to relative visual angle. The results are applied to an analysis of size-matches that are obtained when distance cues are eliminated.     

Spatial memory in rats under restricted viewing conditions

In a procedure devised by J. A. Walker and D. S. Olton (Learning and Motivation, 1979, 10, 73–84), rats were placed on two arms of a four-arm radial maze and then were placed in the center of the maze to test how accurately they could choose the alleys on which they had not been placed. In three experiments, the conditions under which animals viewed the environment from the arms were varied. In Experiment 1, both the extent of spatial view and the exposure time were varied factorially in a within-subjects design; animals viewed the environment down a tunnel or had a 180° or 360° view, and subjects were allowed to view the environment for either 2 or 20 sec. In Experiment 2, a between-subjects design was used, in which different groups of subjects were tested repeatedly under either the tunnel, 180°, or 360° conditions. Both experiments showed that animals could avoid the arms previously visited at no better than a chance level of accuracy in the tunnel viewing condition but could perform with progressively better accuracy at the 180 and 360° viewing conditions. Animals also were more accurate in Experiment 1 after viewing for 20 sec than after viewing for 2 sec. Experiment 3 involved a procedure in which restricted viewing conditions were used both during arm placements and testing. Animals tested under tunnel viewing eventually achieved above-chance performance with this procedure, but did not exceed chance as rapidly as groups tested with 45 and 90° views of the environment. These results suggest that animals can learn about their position in a spatial environment through observation and that an animal's ability to locate its position is directly related to the extent of the surrounding environment it can see and the length of time it is allowed to look. The implications of these findings for list and map hypotheses of spatial memory representation are discussed.     

Adaptation to optically-increased interocular separation under naturalistic viewing conditions

Mirror spectacles which enhance binocular disparity by optically doubling the normal separation between the eyes were used to create conditions of combined perceptual and oculomotor conflict. Apparent depth and distance, as well as tonic accommodation, tonic vergence, and accommodative-vergence gain (response AC/A ratio), were assessed immediately before and after a 30 min exposure period of naturalistic viewing with the spectacles. Wearing the spectacles produced an increase in tonic vergence, and perceptual aftereffects consisting of increased apparent distance and depth. The results indicate that oculomotor conflict associated with enhanced interocular separation may be resolved through adaptation of tonic vergence, rather than through alteration of accommodative-vergence gain. The results also demonstrate that perceptual conflict between disparity and multiple veridical depth cues does not necessarily produce adaptive modification of the relationship between binocular disparity and apparent depth.     

Geometrical illusions in solid objects under ordinary viewing conditions

The Müller-Lyer and Ponzo illusions were obtained under free binocular viewing of three-dimensional objects, and the function relating magnitude of illusion to fin angle, characteristic of converging-line versions of the Müller-Lyer pattern, was closely paralleled by volumetric (three-cone), line-free objects (but not with an erect, planar “walk-through” construction and moving observers). Illusions cannot be dismissed as artifacts of static, impoverished viewing, therefore, but must be explained within any general theory of perception. Perspective explanations have difficulties with such three-dimensional manifestations, and seem completely inapplicable to our further finding that approximately the same amount of illusion occurred in objects and patterns with no oblique lines or edges. Confusion or averaging theories, not themselves tested here, remain unthreatened by these data.     

Goal-directed aiming under restricted viewing conditions with confirmatory sensory feedback

A substantial body of research has examined the speed-accuracy tradeoff captured by Fitts’ law, demonstrating increases in movement time that occur as aiming tasks are made more difficult by decreasing target width and/or increasing the distance between targets. Yet, serial aiming movements guided by internal spatial representations, rather than by visual views of targets have not been examined in this manner, and the value of confirmatory feedback via different sensory modalities within this paradigm is unknown. Here we examined goal-directed serial aiming movements (tapping back and forth between two targets), wherein targets were visually unavailable during the task. However, confirmatory feedback (auditory, haptic, visual, and bimodal combinations of each) was delivered upon each target acquisition, in a counterbalanced, within-subjects design. Each participant performed the aiming task with their pointer finger, represented within an immersive virtual environment as a 1 cm white sphere, while wearing a head-mounted display. Despite visual target occlusion, movement times increased in accordance with Fitts’ law. Though Fitts’ law captured performance for each of the sensory feedback conditions, the slopes differed. The effect of increasing difficulty on movement times was least influential in the haptic condition, suggesting more efficient processing of confirmatory haptic feedback during aiming movements guided by internal spatial representations.     

Geometrical illusions in solid objects under ordinary viewing conditions.

The Müller-Lyer and Ponzo illusions were obtained under free binocular viewing of three-dimensional objects, and the function relating magnitude of illusion to fin angle, characteristic of converging-line versions of the Müller-Lyer pattern, was closely paralleled by volumetric (three-cone), line-free objects (but not with an erect, planar "walk-through" construction and moving observers). Illusions cannot be dismissed as artifacts of static, impoverished viewing, therefore, but must be explained within any general theory of perception. Perspective explanations have difficulties with such three-dimensional manifestations, and seem completely inapplicable to our further finding that approximately the same amount of illusion occurred in objects and patterns with no oblique lines or edges. Confusion or averaging theories, not themselves tested here, remain unthreatened by these data.     

Eye tracking under dichoptic viewing conditions: a practical solution

In several research contexts it is important to obtain eye-tracking measures while presenting visual stimuli independently to each of the two eyes (dichoptic stimulation). However, the hardware that allows dichoptic viewing, such as mirrors, often interferes with high-quality eye tracking, especially when using a video-based eye tracker. Here we detail an approach to combining mirror-based dichoptic stimulation with video-based eye tracking, centered on the fact that some mirrors, although they reflect visible light, are selectively transparent to the infrared wavelength range in which eye trackers record their signal. Although the method we propose is straightforward, affordable (on the order of US$1,000) and easy to implement, for many purposes it makes for an improvement over existing methods, which tend to require specialized equipment and often compromise on the quality of the visual stimulus and/or the eye tracking signal. The proposed method is compatible with standard display screens and eye trackers, and poses no additional limitations on the quality or nature of the stimulus presented or the data obtained. We include an evaluation of the quality of eye tracking data obtained using our method, and a practical guide to building a specific version of the setup used in our laboratories.     

Role of familiar size in spatial judgments under natural viewing conditions.

The purpose of the present experiment was to examine the role of familiar size in judgments of size and egocentric distance under natural (non-reduced) viewing conditions. Independent groups (ns = 14) judged normal and large off-size chairs and control objects presented at a distance of 25.6 m. Subjects also judged the size of unfamiliar objects (adjacent stimuli) attached to the chairs and stakes. The results indicate that the effects of familiar size are specific to spatial judgments of the familiar object itself since judgments of the adjacent stimuli were unaffected by familiar size.     

Difference threshold for intensity of tactile stimuli

The difference threshold (DL) for brief tactile stimuli (taps) and vibrotactile stimuli was determined using a 2IFC procedure. The measurements were made at several intensities both in quiet and in the presence of a background vibration. The results show that in the absence of background vibration the DLs for higher intensity stimuli are similar for both taps and vibration, whereas at lower intensities the DL is larger for taps. In the presence of background vibration the DL for vibratory stimuli is elevated to a much greater extent than it is for tap stimuli. The DL is affected by both the intensity of the signal and the intensity of the background vibration.     

Effect of an auditory stimulus on the processing of a visual stimulus under single- and dual-tasks conditions

The Sternberg Additive Factor Method was used to draw inferences about the flow of information under single- and dual-tasks conditions which were identical in terms of the stimuli involved but different in terms of response requirements. In both conditions, subjects pressed a left- or right-hand key in response to the onset of an X or O (intact or degraded) which was accompanied by a monaural or binaural tone. In the dual-tasks condition, subjects responded verbally to the tone location while also making the key-press response, whereas, in the single-task condition, no response to the tone was required. The pattern of main effects and interactions suggested that the same model of information flow described both single- and dual-tasks conditions; i.e., visual and auditory stimuli were encoded separately but shared capacity at the response selection stage.     

Visual alleys as a function of instructions under informative and reduced conditions of viewing

Three experiments were designed to explore parallel and distance alleys as a function of instructions (apparent and objective) under three different distance-cue conditions. The main findings were that (1) the alleys for the apparent instructions were positioned closer to the median plane than those for the objective instructions, (2) in an indoor setting, the parallel and distance alleys were not different under either the apparent or the objective instructions, and (3) in an outdoor setting, the parallel alley lay inside the distance alley under both the apparent and the objective instructions. On the basis of comparison with some of the previous alley studies, it is suggested that exact control of instructions will not produce great discrepancy between the parallel and the distance alleys that were constructed indoors.     

Watching your troubles away: television viewing as a stimulus for subjective self-awareness

Three studies explored the role of television viewing in eliciting subjective self-awareness and positive self-feelings. Study 1 assessed the effects of self-awareness manipulations via exposure to a neutral television program on actual-ideal discrepancies. Those who watched television showed significantly smaller self-discrepancies than those who did not, independent of mood. Study 2 demonstrated the ecological validity of this finding by replicating it with people watching television in their own homes. Study 3 investigated whether manipulations of self-feelings affected television watching. Results indicated that those who received failure feedback watched television longer than those in a control condition who likewise watched television longer than those who received success feedback. Television appears to be an effective stimulus to direct the focus away from oneself and to render people less aware of how they are falling short of their standards.