July 2013
Volume 13, Issue 9
Free
Vision Sciences Society Annual Meeting Abstract  |   July 2013
Size dependent increase in sensitivity to the slope of the amplitude spectrum is not solely dependent on the increased low spatial frequency representation of larger stimuli.
Author Affiliations
  • Bruno Richard
    Department of Psychology, Concordia University, Montréal, Québec, Canada.
  • Bruce Hansen
    Dept. Psychology & Neuroscience Program, Colgate University, Hamilton, New York, USA.
  • Dave Ellemberg
    Dept. Kinesiology, University of Montreal, Montréal, Québec, Canada.
  • Aaron Johnson
    Department of Psychology, Concordia University, Montréal, Québec, Canada.
Journal of Vision July 2013, Vol.13, 1238. doi:10.1167/13.9.1238
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      Bruno Richard, Bruce Hansen, Dave Ellemberg, Aaron Johnson; Size dependent increase in sensitivity to the slope of the amplitude spectrum is not solely dependent on the increased low spatial frequency representation of larger stimuli.. Journal of Vision 2013;13(9):1238. doi: 10.1167/13.9.1238.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

We have previously investigated if threshold discrepancies between studies that have measured sensitivity to the slope of the amplitude spectrum may be due to differences between stimulus size (Richard et al., VSS 2012). We found that slope discrimination thresholds decreased as stimulus size increased, and concluded that the decrease in thresholds might be due to either the greater spatial summation of contrast in the larger stimuli, or the additional lower spatial frequencies present in larger stimuli. Here, we investigated if the latter can explain the size dependent increase in sensitivity to an amplitude spectrum slope. We used the largest stimulus size from the previous study (11.3°) containing the largest range of spatial frequencies (0.09 – 13.4 cpd), and filtered it with an ideal high-pass filter to mimic the spatial frequency content of smaller stimuli. The stimulus covered approximately 7 octaves (0.09-0.18, 0.18-0.35, 0.35-0.71, 0.71-1.42, 1.42-2.84, 2.84-5.68,5.68-11.36 cpd), and we used 6 high-pass filters (cut-off frequencies 0.12, 0.25, 0.50, 1.00, 2.00, 4.02 cpd). Thresholds did increase as higher spatial frequencies were removed from the stimulus, which indicates lower thresholds are somewhat dependent on the lower spatial frequencies present within larger stimuli. Yet, this increase did not match the decrease in threshold found in the previous study. Our results show that a minimum of three octaves - which represent a stimulus size of about 2° - was required for thresholds to begin increasing. When more than three octaves were present, thresholds remained relatively stable. Slope discrimination is influenced by spatial frequency content of the stimuli, but this does not completely explain the size effect found in the previous study. Therefore, we conclude that spatial summation of contrast may also contribute to the decrease in thresholds found when stimulus size is increased.

Meeting abstract presented at VSS 2013

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