Aging does not decrease spatial suppression in a motion step task
26.442, Saturday, May 11, 2:45 - 6:45 pm, Orchid Ballroom
Lindsay E. Rosen1, Allison B. Sekuler1,2, Patrick J. Bennett1,2; 1McMaster Integrative Neuroscience Discovery & Study (MiNDS) Program, McMaster University, 2Department of Psychology, Neuroscience & Behaviour, McMaster University, 3Centre for Vision Research, York University
Direction discrimination becomes more difficult as high-contrast stimuli increase in size and as low-contrast stimuli decrease in size (Tadin et al., Nature, 2003). However, although older adults show spatial summation at low contrast, they demonstrate no evidence for spatial suppression at high contrast (Betts et al., Neuron, 2005). It has been hypothesized that this behavioural finding occurs as a result of decreased GABAergic inhibition in the aging visual system (Leventhal et al., Science, 2003), but it is unclear whether the finding extends to other tasks; for example, static tasks have not shown the same effects of aging (Karas & McKendrick, J Vis, 2009; Farber et al., VSS 2010 & 2011). Recently, Churan et al. (J Vis, 2009) described results from a motion step task consistent with summation at low contrast and suppression at high contrast for younger subjects, providing us with an opportunity to examine the effects of aging in another paradigm using brief motion stimuli. In the current study, we tested six younger and four older adults in this task. A vertically-oriented 0.5 cpd Gabor stimulus remained static in the center of the screen for 35 ms, and then, after a brief motion step, the phase-shifted gabor was presented for another 35 ms. A 2-down, 1-up staircase manipulated the size of the phase jump (1-89 deg) required to correctly determine the motion direction. There were four blocks, one for each combination of contrast (1.5, 98%) and size (4.56, 17.68 deg). Results from younger subjects replicated the findings from Churan et al. (2009), and older adults also demonstrated this pattern of spatial summation at low contrast and spatial suppression at high contrast. Hence, we found no evidence of an age-related reduction in spatial suppression in this task, suggesting that the phenomenon may be limited even for brief motion stimuli.