Biology subjects

Baumann, M. P.

Publications and source records attributed to Baumann, M. P..

3 recordsLinked to original sources

bioRxiv2020

Dependence of perceptual saccadic suppression on peri-saccadic image flow properties and luminance contrast polarity

Across saccades, perceptual detectability of brief visual stimuli is strongly diminished. We recently observed that this perceptual suppression phenomenon is jumpstarted in the retina, suggesting that the phenomenon might be significantly more visual in nature than normally acknowledged. Here, we explicitly compared saccadic suppression strength when saccades were made across a uniform image of constant luminance versus when saccades were made across image patches of different luminance, width, and trans-saccadic luminance polarity. We measured perceptual contrast thresholds of human subjects for brief peri-saccadic flashes of positive (luminance increments) or negative (luminance decrements) polarity. Perceptual thresholds were >6-7 times higher when saccades translated a luminance stripe or edge across the retina than when saccades were made over a completely uniform image patch. Critically, both background luminance and flash luminance polarity relative to the background strongly modulated peri-saccadic contrast thresholds. In addition, all of these very same visual dependencies also occurred in the absence of any saccades, but with qualitatively similar rapid translations of image patches across the retina. Our results support the notion that perceptual saccadic suppression may be fundamentally a visual phenomenon, and they motivate neurophysiological and theoretical investigations on the role of saccadic eye movement commands in modulating its properties.

neuroscience↗

bioRxiv2020

Retinal mechanisms of saccadic suppression and their role in processing sequential stimuli

Visual perception remains stable across saccadic eye movements, despite the concurrent strongly disruptive visual flow. This stability is partially associated with a reduction in visual sensitivity, known as saccadic suppression, which already starts in the retina with reduced ganglion cell sensitivity. However, the retinal circuit mechanisms giving rise to such suppression remain unknown. Here, we describe these mechanisms using electrophysiology in mouse, pig, and macaque retina, 2-photon calcium imaging, computational modeling, and human psychophysics. We find that sequential stimuli, such as those that naturally occur during saccades, trigger three independent suppressive mechanisms in the retina. The main suppressive mechanism is triggered by contrast-reversing sequential stimuli and originates within the receptive field center of ganglion cells. It does not involve inhibition or other known suppressive mechanisms such as saturation or adaptation. Instead, it relies on temporal filtering of the inherently slow response of cone photoreceptors coupled with downstream nonlinearities. Two further mechanisms of suppression are present predominantly in ON ganglion cells and originate in the receptive field surround, highlighting a novel disparity between ON and OFF ganglion cells. The mechanisms uncovered here likely play a role in shaping the retinal output following eye movements and other natural viewing conditions where sequential stimulation is ubiquitous.

neuroscience↗

bioRxiv2020

Instantaneous movement-unrelated midbrain activity modifies ongoing eye movements

At any moment in time, new information is sampled from the environment and interacts with ongoing brain state. Often, such interaction takes place within individual circuits that are capable of both mediating the internally ongoing plan as well as representing exogenous sensory events. Here we investigated how sensory-driven neural activity can be integrated, very often in the same neuron types, into ongoing oculomotor commands for saccades. Despite the ballistic nature of saccades, visually-induced action potentials in the superior colliculus (SC), a structure known to drive eye movements, not only occurred intra-saccadically, but they were also associated with highly predictable modifications of ongoing eye movements. Such predictable modifications reflected a simultaneity of movement-related discharge at one SC site and visually-induced activity at another. Our results suggest instantaneous readout of the SC map during movement generation, irrespective of activity source, and they explain a significant component of kinematic variability of motor outputs.

neuroscience↗