Monday, March 16,  12:00 – 1:30 pm, in 489 Minor Hall

Graduate Student Seminar

presented by

Adeola Harewood (Silver Lab)

Visual Field Shape, Critical Spacing, and Spatial Attention

Behavioral performance is better in the lower, compared to the upper, visual field for a variety of perceptual tasks, including visual crowding. Recently, Fortenbaugh et al. (2015) presented crowded stimuli along the vertical meridian and showed that this lower visual field advantage can be accounted for by asymmetry in the shape of the visual field along this axis. Specifically, individuals with more asymmetric visual fields along the vertical meridian have a larger lower visual field advantage in a crowding task and this correlation goes away when attention is divided. We are continuing this work by studying visual field asymmetries in critical spacing, the minimum distance between a target and its flankers that is needed to enable a certain level of performance on a crowding task. We are also examining how critical spacing is affected by the interactions between visual field shape and spatial attention. Upper and lower visual field extents were first measured in each participant using a Goldmann perimeter. Participants then completed a crowding task that required them to discriminate the orientation of a target grating in the presence of flankers. We manipulated spatial attention by varying the amount of uncertainty that subjects had about upcoming target locations. I will present data from this study as well as future directions.


Zachary Helft (Kramer Lab)


Mechanism of Selective Action of Photoswitches in the Blind Retina

Retinitis pigmentosa (RP) and age-related macular degeneration (AMD) are blinding diseases caused by the degeneration of photorecepters. This leaves the remaining retinal neural circuitry intact, but unable to respond to light. Retinal prostheses, which directly electrically stimulate these remaining cells, have been introduced into the market, but remain invasive and restore only the most basic of visual responses. In 2008, discoveries in the realm of optogenetics were able to confer light sensitivity to blind mice by expressing light sensitive proteins in the remaining cells in the retina. This approach has the ability to target specific cells to recapitulate contrast channels in the visual information stream. The impact of blinding diseases has been recognized by the NEI, which, as of summer 2013 made “Molecular Therapies for Eye Disease” a priority. Three years ago, the first purely photochemical restoration of visual responses were reported (Polosukhina et al., 2012). After injection of a chemical photoswitch, pupillary light reflexes, light field aversion, and fear conditioning were all restored in response to visual cues in a model of RP, the rd1 mouse line. Photochemical restoration has the advantage of not requiring genetic modification of the host organism and thus is an attractive path for therapeutics targeting RP and AMD. Photoswitches have gone through several generations of development since their inception improving light sensitivity, persistence, and magnitude of response. (Tochitsky et al., 2014) An important aspect of all examined photoswitches is their selective effect upon degenerated retina and selectivity within a degenerated retina for certain types of cells. What about the process of degeneration allows for selective action? The current investigation elucidates the permeability of the ganglion cell layer in degenerated retina by the use of fluorescent dyes and which signaling molecules are responsible for this degeneration.

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