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Wilson Chu, Barbara Anne Dosher, Zhong-Lin Lu; Measuring the accuracy and precision of visual representations in validly and invalidly spatially pre-cued visual working memory. Journal of Vision 2010;10(7):742. doi: 10.1167/10.7.742.
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Valid pre-cuing of spatial attention improves visual identification, especially in the presence of visual noise in the stimulus (Dosher & Lu, 2000). The current study used orientation-report methods to measure the accuracy and precision of stimulus representations in visual working memory (VWM) (Zhang & Luck, 2008) following either a valid or an invalid location pre-cue. Gabor patches of varying contrast appeared at each of four corners at 5 deg eccentricity about fixation. The Gabors were selected from 20 9°-spaced orientations. External noise was added on half the trials, with the contrast of the Gabors adjusted accordingly. One of the four locations was pre-cued 150 ms before the oriented Gabors and then the delayed report-cue appeared 800 ms after the Gabors indicating the to-be-reported location. Observers clicked on a Gabor from a 20-orientation palette to report the orientation. The precision and accuracy of the visual representation was measured through the spread of responses about the orientation of the to-be-reported stimulus. The pre-cue was valid on 5/8 of trials, while another location was cued for report in 3/8 of trials. The reports in validly cued trails, which could have supported encoding earlier in the delay interval, showed higher accuracy and good precision about the correct orientation. Performance in reporting the correct orientation was dramatically reduced in invalidly cued trials, where the report-cued location was unpredictable until 800 ms after the stimulus, and observer's reports were more broadly tuned, incorporating more guessing errors. As in spatially cued attention, invalid cuing was especially damaging in high external noise for a number of observers. Several observers showed very poor performance for invalidly cued trials in high external noise. These data can be considered as a mixture of a good precision encoding and guessing, with the availability of the processes dependent on cuing and on external noise.
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