Biomedical subjects

Joseph B Hopfinger

Publications and source records attributed to Joseph B Hopfinger.

4 recordsLinked to original sources

PubMed2006

Interactions between endogenous and exogenous attention on cortical visual processing.

Sensory processing is affected by both endogenous and exogenous mechanisms of attention, although how these mechanisms interact in the brain has remained unclear. In the present study, we recorded event-related potentials (ERPs) to investigate how multiple stages of information processing in the brain are affected when endogenous and exogenous mechanisms are concurrently engaged. We found that the earliest stage of cortical visual processing, the striate-cortex-generated C1, was immune to attentional modulation, even when endogenous and exogenous attention converged on a common location. The earliest stage of processing to be affected in this experiment was the late phase of the extrastriate-cortex-generated P1 component, which was dominated by exogenous attention. Processing at this stage was enhanced by exogenous attention, regardless of where endogenous attention had been oriented. Endogenous attention, however, dominated a later, higher-order stage of processing indexed by an enhancement of the P300 that was unaffected by exogenous attention. Critically, between these early and late stages, an interaction was found wherein endogenous and exogenous attention produced distinct, and overlapping, effects on information processing. At the same time that exogenous attention was producing an extended enhancement of the late-P1, endogenous attention was enhancing the occipital-parietal N1 component. These results provide neurophysiological support for theories suggesting that endogenous and exogenous mechanisms represent two attention systems that can affect information processing in the brain in distinct ways. Furthermore, these data provide new evidence regarding the precise stages of neural processing that are, and are not, affected when endogenous and exogenous attentions interact.

Adult↗

PubMed2005

Appearing and disappearing stimuli trigger a reflexive modulation of visual cortical activity.

From the vast array of stimuli continually inundating our senses, only a very small portion is selected for higher-order processing. This selection is influenced by voluntary and reflexive mechanisms that may act at multiple stages of analysis. Extensive research has revealed that top-down voluntary mechanisms modulate information processing at both "early" (e.g., perceptual) and "late" (e.g., semantic) stages. Bottom-up sensory-driven mechanisms, however, are less well understood. Previous investigations of bottom-up mechanisms may have been influenced by top-down mechanisms because the stimuli were task-relevant and required overt responses. Here, we directly measured bottom-up influences on visual information processing by recording event-related brain potentials (ERP) to sequences of task-irrelevant visual stimuli. We found that abrupt visual events triggered an automatic enhancement of extrastriate visual activity (the P1 ERP component) to subsequent visual stimuli occurring at the same location. In contrast to theories suggesting that the abrupt appearance of a new object is unique in being able to trigger bottom-up effects, we found that disappearing objects triggered the same enhancement of subsequent stimulus processing as did appearing objects. The present data, however, also provide new electrophysiological evidence for a level of analysis in the brain that may be specific to the appearance of new objects. These data thus provide evidence that abruptly appearing objects may evoke specialized processing at certain stages of analysis in the brain but that, despite this difference, appearing and disappearing objects both trigger reflexive mechanisms that bias neural activity in human extrastriate visual cortex.

Adolescent↗

PubMed2005

Automatic versus contingent mechanisms of sensory-driven neural biasing and reflexive attention.

Recent studies have generated debate regarding whether reflexive attention mechanisms are triggered in a purely automatic stimulus-driven manner. Behavioral studies have found that a nonpredictive "cue" stimulus will speed manual responses to subsequent targets at the same location, but only if that cue is congruent with actively maintained top-down settings for target detection. When a cue is incongruent with top-down settings, response times are unaffected, and this has been taken as evidence that reflexive attention mechanisms were never engaged in those conditions. However, manual response times may mask effects on earlier stages of processing. Here, we used event-related potentials to investigate the interaction of bottom-up sensory-driven mechanisms and top-down control settings at multiple stages of processing in the brain. Our results dissociate sensory-driven mechanisms that automatically bias early stages of visual processing from later mechanisms that are contingent on top-down control. An early enhancement of target processing in the extrastriate visual cortex (i.e., the P1 component) was triggered by the appearance of a unique bright cue, regardless of top-down settings. The enhancement of visual processing was prolonged, however, when the cue was congruent with top-down settings. Later processing in posterior temporal-parietal regions (i.e., the ipsilateral invalid negativity) was triggered automatically when the cue consisted of the abrupt appearance of a single new object. However, in cases where more than a single object appeared during the cue display, this stage of processing was contingent on top-down control. These findings provide evidence that visual information processing is biased at multiple levels in the brain, and the results distinguish automatically triggered sensory-driven mechanisms from those that are contingent on top-down control settings.

Adolescent↗

PubMed2002

Darkness beyond the light: attentional inhibition surrounding the classic spotlight.

The aim of the present investigation was to determine the nature and spatial distribution of selective visual attention. Using cortical source localization of ERP data corresponding to 60 task-irrelevant stimuli across the visual field, we assessed attention effects on visual processing. Consistent with previous findings, visual processing was enhanced at the attended spatial location. In addition, this facilitation of processing extended from the attended location to the point of fixation resulting in a region of facilitation. Furthermore, a large region of inhibition was found surrounding this region of facilitation. The latter result is inconsistent with a simple facilitative spotlight model of attention and indicates that attention effects can be both facilitatory and inhibitory.

Adult↗