Using photorealistic visual images to understand the neuronal integration of visual cues for depth and shape in the ventral stream pathways of the primate brain.

• Applicant: Professor Andrew Parker, Ph.D.
• Subject Area: Cognitive, Systems and Behavioural Neurobiology
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 498049560

The organization of the nervous system for the visual recognition of objects is often thought to be hierarchical. Nerve cells near the top of the hierarchy can typically be activated only by complex and meaningful stimuli, whereas nerve cells low down in the hierarchy are activated by specific distributions of luminance intensities in the image received by the eye. The encoding of information in the high-level stages resembles perception of the object itself, whereas pattern of activity in the earliest stages resembles a simple transformation of the original image.The “hard problem” for visual processing takes place in the critical, intermediate stages, where the transformation from image to object takes place. This project will concern itself with two of these stages in the ventral visual pathways of the macaque cerebral cortex: the fourth visual area (V4) and the posterior inferotemporal (PIT) region. This project will adopt two new technological developments to address the role of these areas in visual processing. First, new designs of microelectrodes will be employed, which allow the recording of up to several hundreds of neurons simultaneously. Second, the project will exploit a new method of creating photorealistic images of recognizable objects, which allows specific manipulation of different sources of information about the size, shape and structure of the viewed object.An important goal is to explore the responses of neurons with full control over the binocular image content. When viewing solid objects, macaque monkeys directly view the object of interest with the most sensitive portion of forward-facing eyes, rotating the two eyes inwards to view near objects, just like humans do. This mode of vision provides information about binocular depth, called stereopsis. My research group has recently studied the responses of V4 and PIT neurons to binocular depth in considerable detail. However, the visual stimuli used for these existing experiments used artificial patterns of dots, which are excellent for isolating the response to binocular depth in a pure form, but do not probe vision with naturalistic stimuli.Prior to the neurophysiological recordings, the macaques will be trained to perform discrimination tasks with the photorealistic images, in which the 3-D shape or configuration of the portrayed object will be subtly altered. This approach will ensure that the animals’ attention is fully engaged with the images and the task, which will allow us to reveal the most sensitive components of the neuronal responses. Full advantage will be taken of the parallel capture of recordings from multiple neurons to test modern theories of information representation in the nervous system.

• DFG Programme: Research Grants