Mahadevan Madhumitha S, Bedell Harold E, Stevenson Scott B
University of Houston, College of Optometry, USA.
University of Houston, College of Optometry, USA.
Vision Res. 2018 Feb;143:89-102. doi: 10.1016/j.visres.2017.11.005. Epub 2017 Dec 8.
Visual spatial attention has been shown to influence both contrast detection and suprathreshold contrast perception, as well as manual and saccadic reaction times (SRTs). Because SRTs are influenced also by stimulus contrast, we investigated if the enhancement of perceived contrast that accompanies attention could account for the shorter SRTs observed for attended targets locations. We conducted two dual-task experiments to assess psychophysical and oculomotor responses to non-foveal targets of various contrast for different spatial-attention-cueing conditions. Cues were either: valid, an arrow at fixation pointing in the direction of the upcoming target; invalid, an arrow pointing in a different direction from the target; or neutral, a small circle instead of an arrow. In both experiments, subjects were instructed to make a saccade to the location of a subsequent, briefly flashed target. In the first experiment, the psychophysical judgment was a two-alternative-forced-choice (2AFC) contrast-detection task, in which subjects reported whether the flashed target was at a near (3°) or far (6°) eccentricity. In the second experiment, the judgment was a contrast matching task, in which subjects reported whether the target's contrast was higher or lower than a remembered standard contrast. The results exhibit a robust, ∼40-50 ms reduction of SRTs with a valid compared to an invalid cue. Cueing effects on contrast detection and matching were small and inconsistent across subjects. Hence, the observed decrease in SRTs could not be accounted for fully by an enhancement in the target's effective contrast due to attention, as attended and unattended targets that were equally detectable or were perceived to have the same suprathreshold contrast showed substantial differences in SRT.
视觉空间注意力已被证明会影响对比度检测和超阈值对比度感知，以及手动和扫视反应时间（SRT）。由于SRT也受刺激对比度的影响，我们研究了伴随注意力出现的感知对比度增强是否可以解释在被关注目标位置观察到的较短SRT。我们进行了两项双任务实验，以评估在不同空间注意力提示条件下，对各种对比度的非中央凹目标的心理物理和眼动反应。提示分为以下几种：有效，注视点处指向即将出现目标方向的箭头；无效，指向与目标不同方向的箭头；或中性，一个小圆圈而非箭头。在两项实验中，受试者都被要求扫视到随后短暂闪现目标的位置。在第一个实验中，心理物理判断是一个二选一强制选择（2AFC）对比度检测任务，受试者报告闪现目标是在近（3°）还是远（6°）的偏心度处。在第二个实验中，判断是一个对比度匹配任务，受试者报告目标的对比度高于还是低于记忆中的标准对比度。结果显示，与无效提示相比，有效提示下SRT稳健地减少了约40 - 50毫秒。提示对对比度检测和匹配的影响较小，且受试者之间不一致。因此，观察到的SRT下降不能完全归因于注意力导致的目标有效对比度增强，因为同样可检测或被认为具有相同超阈值对比度的被关注和未被关注目标在SRT上存在显著差异。
