Neuronal basis of the motion aftereffect reconsidered

Area of Science:

• Neuroscience
• Visual Perception
• Human Brain Imaging

Background:

• Previous fMRI studies linked MT+ response to the motion aftereffect (MAE).
• Attention's influence on MT+ responses could confound MAE interpretations.
• Subjects might naturally attend more to MAE trials than control trials.

Purpose of the Study:

• To investigate if attention confounds fMRI studies of the motion aftereffect (MAE).
• To determine the physiological basis of the MAE by controlling for attention.
• To quantify direction-selective neural populations in human visual areas.

Main Methods:

• fMRI (functional Magnetic Resonance Imaging) was used to measure brain activity.
• Subjects attended to motion in both MAE and control trials to control for attention.
• Direction-selective motion adaptation was employed to induce MAE.
• Speed discrimination thresholds were measured.

Main Results:

• Equal MT+ responses were observed in MAE and control trials when attention was controlled.
• Attention accounted for the entire observed effect in previous studies.
• Direction-selective motion adaptation induced direction-selective imbalances in MT+ responses and earlier visual areas.
• A corresponding asymmetry in speed discrimination thresholds was observed.

Conclusions:

• Attention, not the MAE itself, explained previous MT+ response increases.
• Direction-selective neural population imbalances underlie the MAE.
• These findings quantify direction-selective neurons in human visual areas and provide physiological evidence for MAE mechanisms.