Manipulating the disengage operation of covert visual spatial attention

Attentional capture in schizophrenia: failure to resist interference from motion signals

INTRODUCTION

Patients with schizophrenia show high susceptibility to distraction but the neural mechanisms underlying sensitivity to distraction are not clearly established. We designed a paradigm to assess whether sensitivity to distraction and dorsal stream dysfunction are related in schizophrenia.

METHOD

60 patients, 37 schizotypals, and 58 healthy controls were asked to locate a target square appearing above or below fixation and to ignore a distractor that either moved abruptly (in Experiments 1 and 3) or changed in colour (in Experiment 2). The distractor condition was compared to a baseline condition with no distractor. Resistance to interference was assessed by manipulating the probability of the distractor changing more frequently (50%, 75%, 100%) on one side of fixation.

RESULTS

Patients, schizotypals, and controls showed attentional capture with longer response times when the distractor changed as compared to the baseline condition. In contrast to controls, the magnitude of interference from distractors remained stable for patients and schizotypals across all probability conditions and this was confined to attentional capture by motion, not by colour.

CONCLUSION

We found a similar pattern of results in patients and in schizotypals. Our attentional capture paradigm could help to identify early cognitive impairments in populations at risk to develop schizophrenia. The data are interpreted in terms of dysfunction of frontal control on dorsal stream functions in schizophrenia.

Disengaging attention sets the temporal limit of attentive tracking

At first sight, recent studies investigating the temporal limits of attentive tracking show contradictory outcomes. Attentively tracking an object in an ambiguous apparent motion display can have an upper limit of around 0.4 revolutions per second (rps) [Horowitz, T. S., Holcombe, A. O., Wolfe, J. M., Arsenio, H. C., & DiMase, J. S. (2004). Attentional pursuit is faster than attentional saccade. Journal of Vision, 4, 585-603] or 1rps [Verstraten, F. A., Cavanagh, P., & Labianca, A. T. (2000). Limits of attentive tracking reveal temporal properties of attention. Vision Research, 40, 3651-3664.]. Here, we demonstrate that this difference depends on presentation conditions: an important determinant for the temporal limit of attentive tracking appears to be the duty cycle. Tracking performance at high(er) rates decreases to chance with increasing duty cycle, while at low rates duty cycle hardly has an effect on performance. Results are discussed in terms of (dis)engagement of attention.

Covert orienting of visuospatial attention in the early stages of aging

Electrophysiological and behavioral responses were recorded in healthy young (19-23 years) and older (56-66 years) subjects during the execution of a visuospatial attention task. The objective was to test whether covert orienting of visuospatial attention (COVAT) is sensitive to the early stages of aging. All subjects responded faster to targets following valid than invalid cues. The amplitude of the P1 component of visual event-related potentials (ERP) was larger to targets following central valid cues at all SOAs. Subtle age-related changes were observed in P1 amplitude under peripheral cueing. Furthermore, older subjects presented longer reaction times (RTs) and lower P1 amplitudes regardless of the attention condition.

A competition model of exogenous orienting in 3.5-month-old infants

Four experiments are reported on exogenous (stimulus-driven) orienting in 3.5-month-old infants. A small moving bar embedded in a field of static bars was used to draw the infant's attention to one side of the display or the other. The bars could be either red or green. In all four of these experiments sensitivity to this small moving bar was affected significantly by how unevenly the red and green bars were distributed across the visual field. Sensitivity to the moving bar was lower when most of the red bars were in the field contralateral to this probe suggesting competition between the motion stimulus and contralaterally placed red but not green bars on a small, but significant proportion of trials. This basic effect replicated in four separate experiments and depended coarsely on how unevenly the red and the green bars were distributed across the field. A competition model of exogenous orienting with a winner-take-all rule captured the most important features of the data. The distribution of color within the visual field can bias attention significantly at 3.5 months making it either more or less likely that an infant will detect a moving stimulus.