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Ann M. Skoczenski, Ariella Soffer; Orientation tuning of vernier acuity in human infants and adults. Journal of Vision 2002;2(7):195. doi: 10.1167/2.7.195.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose. Differential responses in cortical orientation channels provide critical information for adults' vernier hyperacuity. Developmental studies suggest that young infants can perform simple orientation discriminations but may not use orientation information efficiently in some tasks. Here we used a masking paradigm to ask the question, does orientation information matter in infants' vernier acuity? Methods. We used steady-state visual evoked potentials to measure vernier acuity in 35 4–6-month-old infants, and 4 adults, with no vision abnormalities. In the baseline condition, vernier offsets appeared and disappeared at a rate of 4 Hz in a 1 c/deg vertical square wave grating (40% luminance contrast). Trial length was 10 seconds, during which offset size decreased in log steps from 20 to 1 arc minutes (5–0.2 arc min for adults). The EEG was digitized and filtered to reveal the amplitude and phase of the 4 Hz evoked response; threshold was estimated from average data of 6–8 trials per condition by extrapolating the amplitude vs. offset function to zero microvolts. In the mask conditions, 1-dimensional luminance noise was effectively superimposed with the baseline vernier stimulus using video frame alternation. The 50% contrast mask contained multiple low spatial frequencies (2 +/− 1.5 c/deg). Mask orientation conditions ranged from −40 to +40 degrees from vertical. Each infant was tested on at least 6 different masks; adults were tested with all 17 masks. Results. In adults, all mask conditions elevated thresholds slightly; as with previous data, maximum masking occurred in the 10–20 degree orientation range. Some individual infants had elevated thresholds only in the 40 degree conditions, but mean thresholds showed little overall masking and no orientation-specific masking in infants. Conclusions. Infants do not use the same orientation information as adults do to detect vernier offsets. This may explain infants' poor vernier acuity relative to adults' acuity.
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