A novel task to measure temporal integration in the human visual system

Visual temporal integration refers to the brain's ability to combine and process visual information over time. This mechanism plays a crucial role in various aspects of visual perception, including motion detection, object recognition, and the perception of temporal patterns. Understanding the temporal integration capabilities of the human visual system provides insights into how our brains construct a unified representation of the visual world from discrete visual inputs. Here, we developed a new task to measure visual temporal integration. Participants were presented with the image of a horizontal sine wave pattern. On each frame the image was recreated and random noise added. The task required the merging of consecutive frames presented in rapid succession, in order to discount the noise and construct the percept of a coherent sine wave pattern. The amount of noise added was systematically varied along the image’s vertical axis and participant were asked to report the vertical position at which they could no longer see the pattern in the flickering noise. This value indicates the amount of information that can be integrated from successive frames. Importantly, on separate trials the duration of the frames was varied from 2 to 1000 ms to obtain a temporal threshold of integration. We found that the visual integration for each frame duration followed a sigmoid function that reached an asymptote at around 120 ms, consistent with previous reports of the temporal dynamics of the human visual system. Notably, some participants showed a sharp decrease in performance when the frames duration was ~100 ms. This effect is consistent with visual entrainment of the brain alpha rhythm to the stimuli, providing further evidence for the role of the alpha rhythm in visual temporal integration. Indeed, alignment of alpha integration cycles with single images would prevent integration of multiple stimuli and impair visual performance.