Intermodal selective attention in monkeys. I: distribution and timing of effects across visual areas. Mehta, A. D., Ulbert, I., & Schroeder, C. E. Cerebral Cortex, 10(4):343-58, 2000.
abstract   bibtex   
This study quantified the magnitude and timing of selective attention effects across areas of the macaque visual system, including the lateral geniculate nucleus (LGN), lower cortical areas V1 and V2, and multiple higher visual areas in the dorsal and ventral processing streams. We used one stimulus configuration and behavioral paradigm, with simultaneous recordings from different areas to allow direct comparison of the distribution and timing of attention effects across the system. Streams of interdigitated auditory and visual stimuli were presented at a high rate with an irregular interstimulus interval (mean of 4/s). Attention to visual stimuli was manipulated by requiring subjects to make discriminative behavioral responses to stimuli in one sensory modality, ignoring all stimuli in the other. The attended modality was alternated across trial blocks, and difficulty of discrimination was equated across modalities. Stimulus presentation was gated, so that no stimuli were presented unless the subject gazed at the center of the visual stimulus display. Visual stimuli were diffuse light flashes differing in intensity or color and subtending 12 degrees centered at the point of gaze. Laminar event-related potential (ERP) and current source density (CSD) response profiles were sampled during multiple paired penetrations in multiple visual areas with linear array multicontact electrodes. Attention effects were assessed by comparing responses to specific visual stimuli when attended versus when visual stimuli were looked at the same way, but ignored. Effects were quantified by computing a modulation index (MI), a ratio of the differential CSD response produced by attention to the sum responses to attended and ignored visual stimuli. The average MI increased up levels of the lower visual pathways from none in the LGN to 0.0278 in V1 to 0.101 in V2 to 0.170 in V4. Above the V2 level, attention effects were larger in ventral stream areas (MI = 0. 152) than in dorsal stream areas (MI = 0.052). Although onset latencies were shortest in dorsal stream areas, attentional modulation of the early response was small relative to the stimulus-evoked response. Higher ventral stream areas showed substantial attention effects at the earliest poststimulus time points, followed by the lower visual areas V2 and V1. In all areas, attentional modulation lagged the onset of the stimulus-evoked response, and attention effects grew over the time course of the neuronal response. The most powerful, consistent, and earliest attention effects were those found to occur in area V4, during the 100-300 ms poststimulus interval. Smaller effects occurred in V2 over the same interval, and the bulk of attention effects in V1 were later. In the accompanying paper, we describe the physiology of attention effects in V1, V2 and V4.
@article{ Mehta_etal00a,
  author = {Mehta, A. D. and Ulbert, I. and Schroeder, C. E.},
  title = {Intermodal selective attention in monkeys. {I:} distribution and
	timing of effects across visual areas},
  journal = {Cerebral Cortex},
  year = {2000},
  volume = {10},
  pages = {343-58},
  number = {4},
  abstract = {This study quantified the magnitude and timing of selective attention
	effects across areas of the macaque visual system, including the
	lateral geniculate nucleus (LGN), lower cortical areas V1 and V2,
	and multiple higher visual areas in the dorsal and ventral processing
	streams. We used one stimulus configuration and behavioral paradigm,
	with simultaneous recordings from different areas to allow direct
	comparison of the distribution and timing of attention effects across
	the system. Streams of interdigitated auditory and visual stimuli
	were presented at a high rate with an irregular interstimulus interval
	(mean of 4/s). Attention to visual stimuli was manipulated by requiring
	subjects to make discriminative behavioral responses to stimuli in
	one sensory modality, ignoring all stimuli in the other. The attended
	modality was alternated across trial blocks, and difficulty of discrimination
	was equated across modalities. Stimulus presentation was gated, so
	that no stimuli were presented unless the subject gazed at the center
	of the visual stimulus display. Visual stimuli were diffuse light
	flashes differing in intensity or color and subtending 12 degrees
	centered at the point of gaze. Laminar event-related potential (ERP)
	and current source density (CSD) response profiles were sampled during
	multiple paired penetrations in multiple visual areas with linear
	array multicontact electrodes. Attention effects were assessed by
	comparing responses to specific visual stimuli when attended versus
	when visual stimuli were looked at the same way, but ignored. Effects
	were quantified by computing a modulation index (MI), a ratio of
	the differential CSD response produced by attention to the sum responses
	to attended and ignored visual stimuli. The average MI increased
	up levels of the lower visual pathways from none in the LGN to 0.0278
	in V1 to 0.101 in V2 to 0.170 in V4. Above the V2 level, attention
	effects were larger in ventral stream areas (MI = 0. 152) than in
	dorsal stream areas (MI = 0.052). Although onset latencies were shortest
	in dorsal stream areas, attentional modulation of the early response
	was small relative to the stimulus-evoked response. Higher ventral
	stream areas showed substantial attention effects at the earliest
	poststimulus time points, followed by the lower visual areas V2 and
	V1. In all areas, attentional modulation lagged the onset of the
	stimulus-evoked response, and attention effects grew over the time
	course of the neuronal response. The most powerful, consistent, and
	earliest attention effects were those found to occur in area V4,
	during the 100-300 ms poststimulus interval. Smaller effects occurred
	in V2 over the same interval, and the bulk of attention effects in
	V1 were later. In the accompanying paper, we describe the physiology
	of attention effects in V1, V2 and V4.}
}

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