Dissociation between saliency signals and activity in early visual cortex

TY - JOUR

T1 - Dissociation between saliency signals and activity in early visual cortex

AU - Betz, Torsten

AU - Wilming, Niklas

AU - Bogler, Carsten

AU - Haynes, John-Dylan

AU - König, Peter

PY - 2013/1/1

Y1 - 2013/1/1

N2 - Saliency is a measure that describes how attention is guided by local stimulus properties. Some hypotheses assign its computation to specific topographically organized areas of early human visual cortex. However, in most stimuli, saliency is correlated with luminance contrast, which in turn is known to correlate with activity in these early areas. Thus, any observed correlation of local activity with saliency might be due to the area encoding luminance contrast. Here we disentangle encoding of local luminance contrast and saliency by using stimuli where the two properties are uncorrelated. First, we conducted an eye-tracking study to verify that both negative and positive contrast modifications located in individual quadrants of the visual field increase saliency. Second, subjects viewed identical stimuli while fMRI signals were recorded. We find that positive contrast modifications induce a robust increase of activity in V1-V3 and hV4. However, negative contrast modifications lead to a reduced (V1, V2) or comparable (V3, hV4) activity level compared to unmodified quadrants. Furthermore, even with linear multivariate pattern-classification techniques, it is not possible to decode the location of the salient quadrant independent of the type of the contrast modification. Instead, decoding of the contrast-modified location is only possible separately for the two modification types in V1-V3. These findings suggest that the BOLD activity in V1-V3 is dominated by contrast-dependent processes and does not include the contrast invariance necessary for the computation of feature-invariant saliency.

AB - Saliency is a measure that describes how attention is guided by local stimulus properties. Some hypotheses assign its computation to specific topographically organized areas of early human visual cortex. However, in most stimuli, saliency is correlated with luminance contrast, which in turn is known to correlate with activity in these early areas. Thus, any observed correlation of local activity with saliency might be due to the area encoding luminance contrast. Here we disentangle encoding of local luminance contrast and saliency by using stimuli where the two properties are uncorrelated. First, we conducted an eye-tracking study to verify that both negative and positive contrast modifications located in individual quadrants of the visual field increase saliency. Second, subjects viewed identical stimuli while fMRI signals were recorded. We find that positive contrast modifications induce a robust increase of activity in V1-V3 and hV4. However, negative contrast modifications lead to a reduced (V1, V2) or comparable (V3, hV4) activity level compared to unmodified quadrants. Furthermore, even with linear multivariate pattern-classification techniques, it is not possible to decode the location of the salient quadrant independent of the type of the contrast modification. Instead, decoding of the contrast-modified location is only possible separately for the two modification types in V1-V3. These findings suggest that the BOLD activity in V1-V3 is dominated by contrast-dependent processes and does not include the contrast invariance necessary for the computation of feature-invariant saliency.

KW - Adult

KW - Attention

KW - Female

KW - Humans

KW - Magnetic Resonance Imaging

KW - Male

KW - Vision, Ocular

KW - Visual Cortex

KW - Visual Fields

KW - Young Adult

U2 - 10.1167/13.14.6

DO - 10.1167/13.14.6

M3 - SCORING: Journal article

C2 - 24317424

VL - 13

JO - J VISION

JF - J VISION

SN - 1534-7362

IS - 14

ER -