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Sam Ling, Taosheng Liu, Marisa Carrasco; The influence of attention on motion selective channels: An equivalent noise approach. Journal of Vision 2006;6(6):519. doi: https://doi.org/10.1167/6.6.519.
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© ARVO (1962-2015); The Authors (2016-present)
Background: Two mechanisms have been proposed to explain how attention affects signal processing: Gain (Signal Enhancement) and Tuning (External Noise Exclusion). In the present study we use Equivalent Noise Analysis in conjunction with the Perceptual Template Model (Lu & Dosher, 1998) to assess how sustained (endogenous) attention affects the gain and tuning of motion selective channels.
Methods: In each trial, observers were shown four moving dot cinematograms (100 ms), presented iso-eccentrically. The motion directions of individual dots were drawn from Gaussian distributions around a direction either upward-left or upward-right. External noise was manipulated by varying the coherence of the dot fields, which was defined as the width of the Gaussian distribution. In the Attended condition a small line at fixation pointed to one of the stimulus locations 350 ms prior to the stimuli presentation, instructing observers to attend the upcoming target location. In the Neutral condition, the same line appeared simultaneously with the stimuli. Observers performed a 2AFC direction discrimination task for the field of dots at the cued location, reporting its global motion direction. To obtain Equivalent Noise functions, we measured direction thresholds for different levels of dot coherence (external noise).
Results: For all observers, attention reduced thresholds at high motion coherence levels (low external noise), but had no impact on low coherence (high external noise). These findings are consistent with a model where attention only increases the gain of the motion selective channel (Signal Enhancement), with no influence on tuning (External Noise Exclusion).
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