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Marisa Carrasco, Sam Ling; When sustained attention impairs contrast sensitivity. Journal of Vision 2006;6(6):1100. doi: 10.1167/6.6.1100.
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© ARVO (1962-2015); The Authors (2016-present)
Background: The vast majority of behavioral and neurophysiological studies have shown that attention enhances stimulus representations. But can this enhancement be held indefinitely? Here we report that, over time, sustained (endogenous) attention can actually impair contrast sensitivity. We assessed the time course of attention's effects on contrast sensitivity. If attention boosts stimulus strength, the strengthened stimulus representation may result in stronger selective adaptation.
Methods: Observers adapted to 4 vertical Gabors (4cpd, counter-phase flickering at 10 Hz, 4° eccentricity), which were presented for varying duration (50–8000ms). Before adapting, observers were shown either a Sustained or Neutral cue. These cues instructed observers either to focus their sustained attention towards one of the adaptor stimuli at an upcoming target location (Sustained), or to distribute attention to all four locations (Neutral). Following a brief ISI (100 ms), observers performed a 2AFC orientation discrimination task on a tilted test Gabor (±2°) appearing at one of four iso-eccentric (4°) locations. Contrast thresholds for the test Gabor were measured using a staircase procedure for each adaptation duration and cue type.
Results: For all observers, in the Neutral condition, contrast sensitivity diminished over time; this finding can be explained by contrast adaptation. More interestingly, our results show that sustained attention initially enhances contrast sensitivity (200–500 ms), but as adaptation duration increases, sustained attention leads to impaired contrast sensitivity compared to the neutral condition (>3000 ms). Given that attention boosts signal strength, we interpret these findings as a consequence of adaptation to an attentionally-enhanced stimulus.
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