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Marlene Poncet, Justin Ales; Dramatic effect of duty-cycle on brain response and motion perception. Journal of Vision 2019;19(10):211c. doi: https://doi.org/10.1167/19.10.211c.
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Perceiving motion relies on the integration of a signal over time and space. These two components of motion have been examined in many behavioural experiments but rarely in relation with neural responses. On the other hand, neuroimaging studies have shown that neural responses are not enhanced for a moving stimulus but surprisingly, are instead inhibited. In this study, we investigated the role of the temporal component in motion perception, and specifically if it explains the inhibition of brain responses. For this, we recorded participants’ electroencephalography while a stimulus was flashed periodically at slow (2.6 Hz), medium (5.2 Hz) or fast (10.4 Hz) frequencies. Such stimulation creates Steady-State Visual Evoked Potentials (SSVEPs) whose amplitudes have been shown to correlate with behaviour. The stimulus was presented either at the same location (flicker condition) or at two alternating locations (moving condition). We also manipulated the duty cycle, that is the proportion of time that the stimulus was presented during a cycle (five duty-cycles were used: 12.5%, 25%, 50%, 75%, 87.5%). Our results show that at 2.6 and 5.2 Hz, increasing duty-cycle decreases SSVEP amplitudes by a factor of up to 5. We also find that the perception of motion increases with longer duty-cycles for moving and, unexpectedly, for flickering stimuli as well. Importantly, we find that SSVEP amplitudes are inversely correlated with behaviourally reported motion perception irrespective of whether the stimulus is actually changing position (although motion ratings are always higher for moving than for flickering stimuli). However, at 10.4 Hz, both SSVEP amplitudes and motion perception are not affected by duty-cycle. Modelling of our data using the motion energy model reveals that stimulus energy cannot account for our findings. In conclusion, our study shows that the temporal component modulates motion perception and plays an important role in inhibiting neural responses.
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