Impact of visual motion adaptation on neural responses to objects and its dependence on the temporal characteristics of optic flow

Abstract

It is still unclear how sensory systems efficiently encode signals with statistics as experienced by animals in the real world and what role adaptation plays during normal behavior. Therefore, we studied the performance of visual motion-sensitive neurons of blowflies, the horizontal system neurons, with optic flow that was reconstructed from the head trajectories of semi-free-flying flies. To test how motion adaptation is affected by optic flow dynamics, we manipulated the seminatural optic flow by targeted modifications of the flight trajectories and assessed to what extent neuronal responses to an object located close to the flight trajectory depend on adaptation dynamics. For all types of adapting optic flow object-induced response increments were stronger in the adapted compared with the nonadapted state. Adaptation with optic flow characterized by the typical alternation between translational and rotational segments produced this effect but also adaptation with optic flow that lacked these distinguishing features and even pure rotation at a constant angular velocity. The enhancement of object-induced response increments had a direction-selective component because preferred-direction rotation and natural optic flow were more efficient adaptors than null-direction rotation. These results indicate that natural dynamics of optic flow is not a basic requirement to adapt neurons in a specific, presumably functionally beneficial way. Our findings are discussed in the light of adaptation mechanisms proposed on the basis of experiments previously done with conventional experimenter-defined stimuli.

Gaze characteristics of freely walking blowflies in a goal-directed task

“…(2) Besides detection of self-movement (Krapp, 2000), LPTCs are thought to be involved in spatial vision by extracting distances from translational optic flow during intersaccadic intervals in free-flying flies Karmeier et al, 2006;Kern et al, 2005;Kern et al, 2006;Liang et al, 2008;Liang et al, 2011;Liang et al, 2012). Because stride-coupled rotations are likely to affect the responses of LPTCs, they might impair the acquisition of spatial information.…”

Impact of stride-coupled gaze shifts of walking blowflies on the neuronal representation of visual targets

“…This characteristic might result from the high contrast of the bar and from the coverage of large parts of the receptive field towards the end of the approach. Moreover, translation-based image motion is an additional feature affecting responses of HSE cells (Liang et al, 2008, 2011, 2012). …”

Texture-defined objects influence responses of blowfly motion-sensitive neurons under natural dynamical conditions

“…We used the latest version of FliMax which is equipped with ultra-bright LEDs (maximal luminance ca. 12,000 cd/m 2 , see Liang et al, 2011) and works with an image update rate of 354 Hz. Due to the limited number of LEDs constituting the FliMax stimulator and the angular distance of LEDs of approximately 2° the stimulus textures get low-pass filtered.…”

“…Similar to previous studies (Liang et al, 2008, 2011, 2012), we calculated the object-induced response increment of the cell signal in the following way: The resting potential was calculated by time-averaging the cell response across a time window of 500 ms prior to motion onset of each stimulus repetition, while the stimulus screen was being lit at half maximal brightness. Intersaccadic responses were determined by subtracting the resting potential from the recorded cell response and then by time-averaging within the time windows for the analysis of the intersaccadic responses ( Figures 3B,C ).…”

“…They were covered with textures different from the background. As in previous studies on the encoding of environmental information during intersaccadic intervals (Liang et al, 2008, 2011, 2012), we made intracellular electrophysiological recordings from horizontal system (HS) cells, a well-known class of LPTCs (Hausen, 1982a,b; Krapp et al, 2001). These cells are strongly activated by forward translational motion which is the most prominent motion component during intersaccadic intervals (Kern et al, 2005; Karmeier et al, 2006).…”