Stimulus‐specific adaptation to visual but not auditory motion direction in the barn owl's optic tectum

Abstract

Whether the auditory and visual systems use a similar coding strategy to represent motion direction is an open question. We investigated this question in the barn owl’s optic tectum (OT) testing stimulus specific adaptation (SSA) to the direction of motion. SSA, the reduction of the response to a repetitive stimulus that does not generalize to other stimuli, has been well established in OT neurons. SSA suggests a separate representation of the adapted stimulus in upstream pathways. So far, only SSA to static stimuli has been studied in the OT. Here we examined adaptation to moving auditory and visual stimuli. SSA to motion direction was examined using repeated presentations of moving stimuli, occasionally switching motion to the opposite direction. Acoustic motion was either mimicked by varying binaural spatial cues or implemented in free-field using a speaker array. While OT neurons displayed SSA to motion direction in visual space, neither stimulation paradigms elicited significant SSA to auditory motion direction. These findings show a qualitative difference in how auditory and visual motion is processed in the OT and support the existence of dedicated circuitry for representing motion direction in the early stages of visual but not the auditory system.

Temporal saliency for motion direction may arise from visual stimulus-specific adaptation in avian midbrain inhibitory nucleus

“…Thus, units for which the sum of SI1 and SI2 is greater than zero is a widely accepted criterion for SSA at the population level (Hershenhoren et al, 2014;Malmierca et al, 2009;Taaseh et al, 2011;Valdes-Baizabal et al, 2017). In addition, recorded units for which both SI1 and SI2 are greater than zero show stronger responses to the first deviant for both directions (Wasmuht et al, 2017). To analyze the population tendency for SSA, population averages were obtained by normalizing each recorded site by the maximum response and computing the mean across recorded sites.…”

“…Although the existence of SSA in the auditory system of many vertebrates has been clearly demonstrated (Parto Dezfouli et al, 2019;Reches and Gutfreund, 2008;Zhai et al, 2019), there have been few reports of visual SSA (Dutta et al, 2016;Netser et al, 2011;Wasmuht et al, 2017). The Imc, which has been demonstrated to play a key role in competitive interactions between spatial stimuli and selective attention (Schryver et al, 2020), is an ideal model for exploring the neural basis of visual SSA.…”

“…The neurons can recover their response strength when a novel direction of motion occurs, showing long-lasting visual SSA for motion direction. Since previous studies showed that SSA can be sensitive to ISI and stimulus speed (Ferger et al, 2018;Hershenhoren et al, 2014;Ogawa and Oka, 2015;Wasmuht et al, 2017), we tested that point by using different ISIs, whilst keeping the direction and duration of motion the same. As shown in Figure 4, variation of ISI did not eliminate visual SSA for Imc neurons, but longer intervals reduced the degree of SSA to specific direction of motion (Figure 4).…”

“…The Imc is known to be the main participant in spatial saliency mapping and, scientific interest in its possible role in temporal saliency mapping is increasing. A previous study in pigeons has shown that the optic tectum displays visual SSA to direction of motion (Wasmuht et al, 2017).…”

“…Adaptation has been shown to exist widely in many vertebrate sensory systems, including the auditory system (Parto Dezfouli et al, 2019;Reches and Gutfreund, 2008;Zhai et al, 2019), and recent research has provided evidence that visual adaptation also exists in the optic tectum of birds (Vinken et al, 2017;Wasmuht et al, 2017). The response of an example Imc unit to a constant order paradigm (Figure 1D) , consisting of a dot moving at 30 degrees/s and a 1 s ISI, is shown in Figure 2A.…”