Biomedical subjects

Walter F Bischof

Publications and source records attributed to Walter F Bischof.

4 recordsLinked to original sources

PubMed2004

Seeing the light: Adapting luminance reveals low-level visual processes in the attentional blink.

It is widely assumed that high-level visual processes subserve the attentional blink (AB). Recent evidence from studies of visual masking during the AB that were designed to directly test the contributions of high-level masking effects, however, have failed to provide empirical support for this position. The implication is that low-level visual processes are crucial to the AB. We tested this idea by manipulating adapting luminance in a standard AB paradigm. Consistent with the involvement of low-level neural mechanisms, the AB effect interacted with adapting luminance such that an AB was revealed only under photopic (light adapted) viewing conditions.

Adaptation, Ocular↗

PubMed2003

Visual masking during the attentional blink: tests of the object substitution hypothesis.

When 2 masked targets are presented in a rapid sequence, correct identification of the 1st hinders identification of the 2nd. Visual masking of the 2nd target plays a critical role during this 2nd-target deficit, or "attentional blink" (AB). The object substitution hypothesis (B. Giesbrecht & V. Di Lollo, 1998) predicts that late-stage visual processes involved in object substitution mediate masking of the 2nd target during AB, whereby stronger masking should produce a more severe deficit. Six experiments are presented, together testing this hypothesis. Although masking by object substitution was observed, it did not interact with the AB. An alternative hypothesis is proposed stating that mostly early-stage visual processes mediate the masking effects that are critical to the AB.

Adult↗

PubMed2003

Spatial navigation in virtual reality environments: an EEG analysis.

Past research has linked theta oscillations (electroencephalographic activity in the 4-8-Hz range) to spatial navigation in rodents and humans, and to the encoding and retrieval of spatial information in rodents. In the present study, electroencephalographic activity was measured while humans navigated through virtual mazes. Results confirmed previous findings that the frequency of theta episodes is directly related to the difficulty of maze navigation. We were also able to show that theta episodes occur most likely at points in a maze where new hallways come into view, or after navigational mistakes have been realized and are being corrected. This indicates that, just as in rodents, theta episodes in humans are related to the encoding and retrieval of spatial information.

Adult↗

PubMed1990

On the relation between metacontrast masking and suppression of visible persistence.

Does the introduction of additional contours in a display sequence (an operation known to reduce the strength of suppression in metacontrast) also reduce suppression of visible persistence? In three experiments, duration of visible persistence was estimated by a method in which successful performance depends on the temporal integration of a pattern whose elements are displayed in two successive frames. In this procedure, the arrival of the trailing frame is known to exert a suppressive influence on the visible persistence of the leading frame. Embedding the elements of the leading frame within additional contours (a line grid) reduced the degree of suppression exerted by the trailing frame. This did not occur when the grid was part of the trailing display. We conclude that suppression of visible persistence and metacontrast masking belong to the same class of events.

Adult↗