Perception of geometrical arrays tachistoscopically exposed in right and left visual fields.

Geometrical stimuli (48 6-item arrays of familiar forms, e.g., circle), tachistoscopically presented in the right or left visual field, were more accurately perceived in the right than left visual field by 15 college students. Targets about half the length of the displays exposed here were perceived with equal facility in both visual fields (Bryden, 1960). Results suggest that length of array might affect the difference in perceptual accuracy of forms shown in the right and left visual fields. Figures in the right visual field were predominantly processed from left to right, and forms in the left visual field from right to left. Since more symbols were identified in the right than left visual field, the left to right encoding sequence may be more efficient than a right to left movement. Limited experience of most Ss in reading symbols from left to right is probably only one factor. Extensive experience reading alphabetical material from left to right might have developed the physiological mechanism underpinning this sequence more than the one serving the opposite movement.     

Perception of words and non-words in the upper and lower visual fields

The findings of previous investigations into word perception in the upper and the lower visual field (VF) are variable and may have incurred non-perceptual biases caused by the asymmetric distribution of information within a word, an advantage for saccadic eye-movements to targets in the upper VF and the possibility that stimuli were not projected to the correct retinal locations. The present study used the Reicher-Wheeler task and an eye-tracker to show that, using stringent methodology, a right over left VF advantage is observed for word recognition, but that no differences were found between the upper and the lower VF for either word or non-word recognition. The results are discussed in terms of the neuroanatomy and perceptual abilities of the upper and the lower VF and implications for other studies of letter-string perception in the upper and the lower VF are presented.     

Imagined body orientation and perception of the visual vertical

The existence of body orientation mental imagery was tested by examining whether self roll tilt imagery affects the subjective visual vertical (SVV). Twenty healthy subjects judged the orientation of a dim luminous bar with respect to gravitational vertical, while normally seated in complete darkness with their head firmly restrained earth vertically. SVV was measured in three conditions: a reference condition with no imagery, and a left and a right imagery condition, during which the bar orientation was to be judged while the subjects imagine themselves roll-tilted towards left or right, respectively. The imagined roll tilts were of the same magnitude as roll tilts which generally induce an E- effect, i.e., an SVV lean toward the side opposite to those of body tilt. If imagery and perception of self roll tilt share common processes, self roll tilt imagery should induce an E-like effect. Results show an imagery- induced E-like effect, which strongly supports the idea that humans can perform mental imagery of body orientation about gravity. Received: 4 April 2000 / Accepted: 1 September 2000     

Interaction between eye and body movements to perform visual tasks in upright stance

Synergistic interactions between visual and postural behaviors were observed in a previous study during a precise visual task (search for a specific target in a picture) performed upright as steady as possible. The goal of the present study was to confirm and extend these novel findings in a more ecological condition with no steadiness requirement. Twelve healthy young adults performed two visual tasks, i.e. a precise task and a control task (free-viewing). Center of pressure, lower back, neck, head and eye movements were recorded during each task. The subjective cognitive workload was assessed after each task (NASA-TLX questionnaire). Pearson correlations and cross-correlations between eyes (time-series, characteristics of fixation) and center of pressure/body movements were used to test the synergistic model. As expected, significant negative Pearson correlations between eye and head-neck movement variables were only observed in searching. They indicated that larger precise gaze shifts were correlated with lower head and neck movements. One cross-correlation coefficient (between COP on the AP axis and eyes in the up/down direction) was also significantly higher, i.e. stronger, in searching than in free-viewing. These synergistic interactions likely required greater cognitive demand as indicated by the greater NASA-TLX score in searching. Moreover, the previous Pearson correlations were no longer significant after controlling for the NASA-TLX global score (thanks to partial correlations). This study provides new evidence of the existence of a synergistic process between visual and postural behaviors during visual search tasks.     

Perception of emotional tears with body postures,visual scenes,and written scenarios

Emotional tears tend to increase perceived sadness in facial expressions. However, it is unclear whether tears would still be seen as an indicator of sadness when a tearful face is observed in an emotional context (e.g., a touching moment during a wedding ceremony). We examine the influence of context on the sadness enhancement effect of tears in three studies. In Study 1, participants evaluated tearful or tearless expressions presented without body postures, with emotionally neutral postures, or with emotionally congruent postures (i.e., postures indicating the same emotion as the face). The results show that the presence of tears increases the perceived sadness of faces regardless of context. Similar results are found in Studies 2 and 3, which used visual scenes and written scenarios as contexts, respectively. Our findings demonstrate that tears on faces reliably indicate sadness, even in the presence of contextual information that suggests non-sadness emotions.     

Commentary on high-performance computing and human vision I: Perception of visual space

The presentation by Kersten (1997) demonstrated that changes in the shadow cast by an object are sufficient to produce perception of that object moving in depth. Cutting (1997) characterized many of the pictorial depth cues first described by Leonardo da Vinci. In generating effective virtual reality, we need to understand these perceptual cues.     

Contribution of somesthetic cues to the perception of body orientation and subjective visual vertical

Without relevant visual cues, the subjective visual vertical (SVV) is biased in roll-tilted subjects toward the body axis (Aubert or A-effect). This study focused on the role of the somatosensory system with respect to the SVV and on whether somesthetic cues act through the estimated body tilt. The body cast technology was used to obtain a diffuse tactile stimulation. An increased A-effect was expected because of a greater underestimation of the body position in the body cast. Sixteen subjects placed in a tilt chair were rolled sideways from 0 degrees to 105 degrees. They were asked to verbally indicate their subjective body position and then to adjust a luminous line to the vertical under strapped and body cast conditions. Results showed a greater A-effect (p < .001) but an overestimation of the body orientation (p < .01) in the body cast condition for the higher tilt values (beyond 60 degrees). Since the otolith organs produced the same gravity response in both conditions, errors were due to a change in somesthetic cues. Visual and postural errors were not directly related (no correlation). However, the angular distance between the apparent body position and the SW remained stable, suggesting that the change in somatosensory pattern inputs has a similar impact on the cognitive processes involved in assessing the perception of external space and the sense of self-position.     

Lexical discrimination and letter-string identification in the two visual fields.

Right-handed subjects were tachistoscopically presented three-letter words and nonword permutations in a single visual field for 20 msec. Although the subjects were unable to identify the stimuli at this exposure duration, their lexical decisions were better than chance, and were superior in the left visual field. When the exposure duration was increased, subjects demonstrated superior identification of the words in the right visual field. Results are discussed within an information processing framework.     

The role of categorization in visual search for orientation.

Visual search for 1 target orientation is fast and virtually independent of set size if all of the distractors are of a single, different orientation. However, in the presence of distractors of several orientations, search can become inefficient and strongly dependent on set size (Exp. 1). Search can be inefficient even if only 2 distractor orientations are used and even if those orientations are quite remote from the target orientation (e.g. 20 degrees or even 40 degrees away, Exp. 2). Search for 1 orientation among heterogeneous distractor orientations becomes more efficient if the target orientation is the only item possessing a categorical attribute such as steep, shallow (Exp. 3), tilted left or tilted right (Exp. 4), or simply tilted (Exps. 5 and 6). Orientation categories appear to be 1 of several strategies used in visual search for orientation. These serve as a compromise between the limits on parallel visual processing and the demands of a complex visual world.