Retinotopy

Summary

Retinotopy (from Greek τόπος, place) is the mapping of visual input from the retina to neurons, particularly those neurons within the visual stream. For clarity, 'retinotopy' can be replaced with 'retinal mapping', and 'retinotopic' with 'retinally mapped'. Visual field maps (retinotopic maps) are found in many amphibian and mammalian species, though the specific size, number, and spatial arrangement of these maps can differ considerably. Sensory topographies can be found throughout the brain and are critical to the understanding of one's external environment. Moreover, the study of sensory topographies and retinotopy in particular has furthered our understanding of how neurons encode and organize sensory signals. Retinal mapping of the visual field is maintained through various points of the visual pathway including but not limited to the retina, the dorsal lateral geniculate nucleus, the optic tectum, the primary visual cortex (V1), and higher visual areas (V2-V4). Retinotopic ma

Official source

https://en.wikipedia.org/wiki/Retinotopy

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Neural correlates of non-retinotopic visual processing and light adaptation

Yvonne Evelina Thunell

In the main part of this thesis, I investigate the neural correlates of nonretinotopic processing. We might intuitively think of the visual representation of the world as retinotopic, as is the case for the organization of most visual brain areas, but in fact our perception is usually not retinotopic. Consider for example a bicycle passing by with a reflector on one of its wheels. The reflector appears to move in a circular or prolate cycloidal orbit. It’s true motion trajectory, however, is a curtate cycloid. It seems that we perceive the reflector motion relative to the bicycle. The bicycle thus serves as a moving reference system for computing the motion of its constituent parts. Only little is known about the neural correlates of this type of non-retinotopic processing. Here, using EEG, I investigate the temporal dynamics of the encoding of non-retinotopic motion relative to a moving reference system. The results indicate that the motion of the reference system is discounted from the motion of the part already from 120 ms after stimulus onset and that the non-retinotopic representation dominates throughout the rest of the visual processing. Further, I use fMRI to show that the earliest area in the visual hierarchy holding non-retinotopic representations is the human motion processing complex (hMT+). In the second part of the thesis, the EEG correlates of light adaptation are investigated. Light adaptation is crucial for coping with the large range of ambient luminance values in our environment. We first confirm the known adaptation effect; the overall response to light flashes decreases substantially after adaption to bright light as compared to dim light. Furthermore, this adaptation effect depends on the wavelength of the light, being most pronounced for red light as compared to white, green and blue light. In addition, at short latencies (less than 100 ms) responses to light flashes are stronger after bright than after dim light adaptation for all colors except red. Our results show that even very short-latency EEG responses are differentially affected by different wavelengths of light.

EPFL2014

Motion and tilt aftereffects occur largely in retinal, not in object, coordinates in the Ternus-Pikler display

Marco Boi, Michael Herzog

Recent studies have shown that a variety of aftereffects occurs in a non-retinotopic frame of reference. These findings have been taken as strong evidence that remapping of visual information occurs in a hierarchic manner in the human cortex with an increasing magnitude from early to higher levels. Other studies, however, failed to find non-retinotopic aftereffects. These experiments all relied on paradigms involving eye movements. Recently, we have developed a new paradigm, based on the Ternus-Pikler display, which tests retinotopic vs. non-retinotopic processing without the involvement of eye movements. Using this paradigm, we found strong evidence that attention, form, and motion processing can occur in a non-retinotopic frame of reference. Here, we show that motion and tilt aftereffects are largely retinotopic.

Association for Research in Vision and Ophthalmology2011

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In human vision, the optics of the eye map neighboring points of the environment onto neighboring photoreceptors in the retina. This retinotopic encoding principle is preserved in the early visual areas. Under normal viewing conditions, due to the motion of objects and to eye movements, the retinotopic representation of the environment undergoes fast and drastic shifts. Yet, perceptually our environment appears stable suggesting the existence of non-retinotopic representations in addition to the well-known retinotopic ones. Here, we present a simple psychophysical test to determine whether a given visual process is accomplished in retino- or non-retinotopic coordinates. As examples, we show that visual search and motion perception can occur within a non-retinotopic frame of reference. These findings suggest that more mechanisms than previously thought operate non-retinotopically. Whether this is true for a given visual process can easily be found out with our "litmus test."

Association for Research in Vision and Ophthalmology2009

Neural correlates of non-retinotopic visual processing and light adaptation

Yvonne Evelina Thunell

EPFL2014