Our study aimed to explore the effects of aging on early stages of cortical spatial processing by measuring collinear facilitation using a three-vertically-aligned Gabor stimulus, similar to that used by Polat and Sagi (
1993). The distance between elements (interelement distance [IED]) was taken as a measure of spatial processing. Polat and Sagi (
1993) reported a sharp increase in the contrast detection threshold of the central Gabor at small IEDs (masking). Facilitation was present at IEDs beyond 2
λ (where lambda is the reciprocal of the spatial frequency of the Gabor), with peak facilitation occurring at approximately 3
λ for their stimulus configuration. Our first hypothesis was that the IED for peak facilitation would change with age. The observation that more closely spaced elements were required for the detection of a contour from a noise background (Del Viva & Agostini,
2007) and for discriminating between shapes comprised of elements (McKendrick et al.,
2010), suggests that the distance over which spatial interactions occur is shorter in older observers, at least when all the elements are suprathreshold. An alternate possibility is that neural dropout with age and subsequent cortical rewiring in V1 might result in an increased distance of the lateral connections that underpin collinear facilitation (Connor, Diamond, & Johnson,
1980; Peters, Moss, & Sethares,
2001), hence the critical distance for peak facilitation could instead increase in the elderly. Because the lateral extent of receptive field properties of cortical visual neurons alters with the contrast of the stimulus presented to the receptive field center (Kapadia, Westheimer, & Gilbert,
1999; Sceniak, Hawken, & Shapley,
2002; Sceniak, Ringach, Hawken, & Shapley,
1999; Wielaard & Sajda,
2005), the results of previous studies of suprathreshold spatial interactions do not allow for direct interpretation of the likely outcomes for the threshold task of collinear facilitation.