Positive expiratory pressure as a method for preventing the impairment of attentional processes by hypoxia.

This study investigated the effects of hypoxia on parallel/preattentional and serial/attentional processes in early vision, and the use of a positive-end-expiratory-pressure (PEEP) to prevent the impairment in performance. Twenty-one subjects were submitted to an 8-h hypoxia exposure in a hypobaric chamber (4500 m, 589 hPa, 22 degrees C), both with and without a 5-cm H2O PEEP. Subjects carried out a visual search task consisting of detecting a target among distractors in normoxia, in acute and in prolonged hypoxia. Conjointly their sensitivity to acute mountain sickness (AMS) was scored through the Lake Louise AMS scoring system. Results showed that prolonged hypoxia slowed serial/attentional processing whereas parallel/preattentional processes were not impaired either by acute or by prolonged hypoxia. PEEP prevented serial/attentional processes from slowing and those effects were more clearly observed in the AMS sensitive subjects with respect to the AMS insensitive subjects. These results suggest that the slowing induced by prolonged hypoxia is specific to an early visual process that pilots the scanning of an attentional spotlight throughout the visual field.

Differences in visual search tasks between congenitally deaf and normally hearing adults.

In order to study the processes of central vision in deaf subjects, 12 congenitally deaf adults and 12 normally hearing adults performed a visual search task. The task consisted of detecting a "Q" target among "O" distractors in variable numbers and the reverse. The method used a paradigm based on the stimulus onset asynchrony (SOA) specifically designed to measure the visual processing time between the visual array and a mask. A different visual search pattern was observed in each group. The hearing subjects showed an asymmetrical visual search pattern (parallel versus serial processing respectively for "Q" and "O" targets). In contrast, the deaf subjects showed a symmetrical search pattern (parallel processing in both experimental conditions). In a visual task selectively supported by central vision, visual processes of the congenitally deaf are more efficient when the task involves the contribution of serial processes.

Effect of gravito-inertial cues on the coding of orientation in pre-attentive vision.

To see if the spatial reference frame used by pre-attentive vision is specified in a retino-centered frame or in a reference frame integrating visual and nonvisual information (vestibular and somatosensory), subjects were centrifuged in a non-pendular cabin and were asked to search for a target distinguishable from distractors by difference in orientation (Treisman's "pop-out" paradigm [1]). In a control condition, in which subjects were sitting immobilized but not centrifuged, this task gave an asymmetric search pattern: Search was rapid and pre-attentional except when the target was aligned with the horizontal retinal/head axis, in which case search was slow and attentional (2). Results using a centrifuge showed that slow/serial search patterns were obtained when the target was aligned with the subjective horizontal axis (and not with the horizontal retinal/head axis). These data suggest that a multisensory reference frame is used in pre-attentive vision. The results are interpreted in terms of Riccio and Stoffregen's "ecological theory" of orientation in which the vertical and horizontal axes constitute independent reference frames (3).

Effect of gravitational cues on visual search for orientation.

To determine whether nonvisual (vestibular and somatosensory) information participates in low-level orientation processing, subjects in different postural conditions (upright, supine, and sitting immobilized) searched for a target distinguishable from distractors by difference in orientation (A. Treisman's, 1985, "pop-out" paradigm). Searches for vertical and horizontal targets were dramatically modified as a function of the postural position, indicating that the processing of orientation in early vision is not only retinal but integrates information from the sensory graviceptors. This visuovestibular phenomenon is interpreted in the conceptual framework of D. H. Foster and P. A. Ward's (1991a) model based on local orthogonal orientation filters and T. A. Stoffregen and G. E. Riccio's (1988) dynamics of balance theory.