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Yu-Hsin Yeh, Chien-Chung Chen, Christopher Tyler; Spatial Summation in Noise. Journal of Vision 2018;18(10):207. doi: https://doi.org/10.1167/18.10.207.
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We investigated the effect of background noise on visual spatial summation. We measured the contrast detection threshold of a Gabor target with or without the presence of a white noise mask (4' pixel size) which varied in luminance contrast. The targets were Gabor patterns placed at 3-degree eccentricity to the left or the right of the fixation point and elongated along an arc of the same radius to ensure that every point on the long axis of the stimuli was equal-distance from the fixation. We used a spatial two-alternative forced choice (2 AFC) paradigm, in which the task of an observer in each trial was to indicate whether the target was presented to the left or the right of the fixation. We used the PSI dynamic staircase procedure to measure the threshold at 75% accuracy. Each threshold reported was an average of 4 repeat measurements. When the target size was small (< 36' half-high full width, HHFW), the detection threshold decreased with target size with slope -1 on log-log coordinates, and then further decreased with slope -1/2 till around 72'-100' HHFW, defining the range of attentional summation (Tyler & Chen, 2001). For the same observer, the summation curves at different noise contrasts were shifted copy of each other. The target threshold was constant for noise level up to -26dB (target HHFW=14') or -18 dB (all other target sizes), then increased linearly with noise contrast on log-log coordinates. Since the "elbow" of the target threshold vs. noise intensity function indicates the level of the equivalent internal noise, our result suggests that while the internal noise increases with target size in the full summation range (up to 36' HHFW), it remains constant across target size in the attentional summation range.
Meeting abstract presented at VSS 2018
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