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Souta Hidaka, Masayoshi Nagai, Patrick J. Bennett, Allison B. Sekuler, Jiro Gyoba; Impaired luminance detection in apparent motion trajectory. Journal of Vision 2009;9(8):687. doi: 10.1167/9.8.687.
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Yantis & Nakama (1998) found that letter discrimination was impaired when the letter fell within the path of an apparent motion (AM) trajectory of a spot. Thus, the internal representation of AM stimuli can interfere with perception at a relatively high processing stage (letter discrimination). Here, we investigated whether AM interference also occurs at an earlier processing stage (pattern detection). We presented two square inducers (1×1 deg) at 5 deg below a fixation cross, separated horizontally by 5 deg. The inducer durations and interstimulus intervals (ISIs) were 106 ms. Background luminance was 30 cd/m2; the inducers' Weber contrast was 100%. In the On-AM-path condition, a target of identical shape and dimension as the inducers was presented for 26 ms in-between inducers. In the Off-AM-path condition, the vertical positions of the target and inducers differed by 2 deg. In the FL condition, the inducers flickered so that AM was not perceived. Five observers conducted a target detection task. Two interleaved staircases varied target contrast across to estimate the 50 % detection threshold. We found that threshold in the On-AM-path condition was higher (contrast: 37.9 %) than threshold in the Off-AM-path (contrast: 17.1 %) and FL (contrast: 13.3 %) conditions. Similar results were obtained when the inducers and target had negative contrasts (On-AM-path: −53.3 %; Off-AM-path: −19.2 %; FL: −15.8 %), and when the contrast of the target was negative and that of the inducers was positive (On-AM-path: −27.6 %; Off-AM-path: −13.5 %; FL: −15.9 %). These findings suggest that AM stimuli affect early visual processes involved in detecting a luminance increment or decrement and that the internal representation of AM stimuli reflects the stimulus's attribute (contrast polarity).
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