Several studies report reduced, or a trend for reduced, surround suppression on the motion direction discrimination task in healthy older adults relative to younger adults as demonstrated by shorter duration thresholds for larger, higher contrast stimuli in the older adult group. 12 This task is widely considered as a perceptual analogue of neuronal surround suppressive mechanisms in visual cortex (possibly specifically the middle temporal area MT 13- 15), where suppression is driven by a combination of local feedforward and areal feedback mechanisms to the neuronal receptive field surround. 12 Increasing the size of a high-contrast Gabor stimulus makes it more difficult to correctly determine its motion direction, as demonstrated by an increase in duration thresholds. 9- 11 To investigate perceptual surround suppression of motion, a commonly used task is a motion discrimination procedure which measures the stimulus duration required to accurately determine the direction of motion of Gabor patches of varying sizes and contrasts. 3- 7 For moving stimuli, spatial suppression is considered to assist the visual system to segregate different moving objects from their backgrounds 8 and to provide cues in mid-peripheral vison to subsequently direct saccadic eye movements to objects of interest. 1, 2 One specific aspect of visual function altered by ageing is perceptual spatial suppression, otherwise known as centre-surround suppression. The process of ageing results in wide ranging changes to visual function. When considered alongside previous evidence for reduced suppression for central fixation, our study provides evidence for substantial differences between foveal and parafoveal mechanisms of spatial suppression. Older adults require significantly longer than younger adults to correctly identify stimulus motion, and demonstrate increased spatial suppression of motion, in peripheral vision.
Dividing attention elevated thresholds for both age groups to a similar extent (main effect of attention: p = 0.002), but did not specifically alter spatial interactions (group x attention interaction: p = 0.13). Older adults showed increased spatial suppression of motion relative to younger adults for both tasks (main effect of group: p < 0.001).
#Stimulus duration framen psychopy serial
Twenty younger (19–34 years) and 18 older (61–77 years) adults completed a single task, where observers identified the direction of a drifting Gabor patch of variable size (σ of the Gaussian envelope = 0.5, 1, 2, 3, 4°) presented at 10 degrees of visual angle while observing a central fixation marker, and a dual task, where observers were required to divide their attention across two stimuli, the peripheral drifting Gabor patch and a central rapid serial visual presentation (RSVP) stream. Our study was designed to explore whether spatial suppression of motion is similarly reduced for older adults in parafoveal regions and whether divided attention impacts on suppression strength because attention is known to impact on spatial interactions. Previous studies have shown that such spatial suppression of motion is reduced in older adults in central vision, to the extent that older adults can have better sensitivity than younger adults for foveally presented stimuli. Spatial suppression of motion is considered important to the segmentation of moving objects in the visual environment. It is more difficult to perceive the direction of motion of larger, high contrast patterns than smaller, low contrast patterns due to spatial suppression.
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