Direction-selective ganglion cells in primate retina: a subcortical substrate for reflexive gaze stabilization?
To maintain a stable and clear image of the world, our eyes reflexively follow the direction in which a visual scene is moving. Such gaze stabilization mechanisms reduce image blur as we move in the environment. In non-primate mammals, this behavior is initiated by ON-type direction-selective ganglion cells (ON-DSGCs), which detect the direction of image motion and transmit signals to brainstem nuclei that drive compensatory eye movements. However, ON-DSGCs have not yet been functionally identified in primates, raising the possibility that the visual inputs that drive this behavior instead arise in the cortex. In this talk, I will present molecular, morphological and functional evidence for identification of an ON-DSGC in macaque retina. The presence of ON-DSGCs highlights the need to examine the contribution of subcortical retinal mechanisms to normal and aberrant gaze stabilization in the developing and mature visual system. More generally, our findings demonstrate the power of a multimodal approach to study sparsely represented primate RGC types.
Looking and listening while moving
In this talk I’ll discuss our recent work on how visual and auditory cues to space are integrated as we move. There are at least 3 reasons why this turns out to be a difficult problem for the brain to solve (and us to understand!). First, vision and hearing start off in different coordinates (eye-centred vs head-centred), so they need a common reference frame in which to communicate. By preventing eye and head movements, this problem has been neatly sidestepped in the literature, yet self-movement is the norm. Second, self-movement creates visual and auditory image motion. Correct interpretation therefore requires some form of compensation. Third, vision and hearing encode motion in very different ways: vision contains dedicated motion detectors sensitive to speed, whereas hearing does not. We propose that some (all?) of these problems could be solved by considering the perception of audiovisual space as the integration of separate body-centred visual and auditory cues, the latter formed by integrating image motion with motor system signals and vestibular information. To test this claim, we use a classic cue integration framework, modified to account for cues that are biased and partially correlated. We find good evidence for the model based on simple judgements of audiovisual motion within a circular array of speakers and LEDs that surround the participant while they execute self-controlled head movement.