Poster No:
2065
Submission Type:
Abstract Submission
Authors:
Leyla Loued-Khenissi1, Elsa Scialom2, Michael Herzog2, Bogdan Draganski3
Institutions:
1Lausanne University Hospital, Lausanne, Vaud, 2Laboratory of Psychophysics, BMI, Ecole Polytechnique de Lausanne (EPFL), Lausanne, Switzerland, Lausanne, Vaud, 3Department of Neurology, Inselspital, Bern University Hospital, University of Bern, Bern, Switzerlan, Bern, Bern
First Author:
Co-Author(s):
Elsa Scialom
Laboratory of Psychophysics, BMI, Ecole Polytechnique de Lausanne (EPFL), Lausanne, Switzerland
Lausanne, Vaud
Michael Herzog, PhD
Laboratory of Psychophysics, BMI, Ecole Polytechnique de Lausanne (EPFL), Lausanne, Switzerland
Lausanne, Vaud
Bogdan Draganski
Department of Neurology, Inselspital, Bern University Hospital, University of Bern, Bern, Switzerlan
Bern, Bern
Introduction:
The development of useful cortical prosthesis for the visually impaired is a long-held dream whose current state lags considerably behind its promise. The aim of the concept is to artificially stimulate the brain's visual cortex in individuals suffering from visual impairment and induce sight by way of a cortical implant. Research and development on cortical visual prosthesis have encountered considerable challenges. To date, artificial visual stimulation has focused on the V1 area of the visual cortex, which responds to low-level visual stimuli. Such stimulation induces the appearance of dots of light (phosphenes), however, technical constraints on the number of electrodes that can be implanted in the brain result in a sparse phosphene elicitation, insufficient for object recognition. Targeting brain regions involved in mid-level visual processing, such as lines and curves, might provide a solution by enabling object recognition with fewer electrodes.
Area V4, which plays a key role in processing mid-level visual features, could be a better target for stimulation. To test this hypothesis, we compared neural responses to objects represented as sparse point fragments (phosphenes) and curve segment fragments.
Methods:
We hypothesized that successful object recognition with curve segments would evoke a different pattern of neural response relative to that of phosphenes. We further hypothesized that viewing objects in curve segments relative to phosphene conformation would elicit a significant response in V4, in contrast to phosphenes. To address this question, we administered an object recognition task during fMRI in 23 healthy participants. Objects in the task were taken from the Bank of Standardized Stimuli and consisted of common objects. These objects were transformed into outlines of either phosphenes (dots) or curve segment fragments at the following fragment density levels: 12%, 16%, 21%, 27%, 35%, 46%, 59% and 77%, following an exponential fit previously used in (Torfs et al., 2010). Fragments were presented in white on a black background at 7 different levels of fragment density. At each trial, an object was briefly presented for 120 ms. Participants were then shown a 3x3 grid of RGB objects and asked to select the one they had previously seen, and then asked to provide a measure of confidence in their performance. In total, participants performed a total of 144 trials separated into two blocks. Eight distinct objects were selected as target stimuli and an additional 12 were selected as decoys.
Results:
We find that a correct recognition of objects composed of segment relative to phosphene fragments elicited widespread significant responses at the whole brain level in cortical areas, including the superior and middle temporal gyri, anterior cingulate, anterior insula , precentral, postcentral and supramarginal gyri, and superior parietal lobule. A region-based analysis on areas V1, V4 and lateral occipital cortex (a region implicated in object recognition), showed that, while phosphenes evoked significant responses in both V1 and LOC, curve segments relative to phosphenes elicited both V1 and V4 responses. Main onsets of interest included fragmented object presentation, separated into phosphene and curve segment conditions.
Conclusions:
The implications of our results are twofold. First, object recognition of curve segment fragments engages a network of higher-level cortical areas when compared to object recognition of phosphene fragments, highlighting differences and possibly downstream cognitive strategies in the perceptual resolution of objects represented by curve segments. Second, while area V1 responds to both low- and mid-level visual stimulus features, area V4 specifically responds to correct object recognition of mid-level stimulus features only. These results suggest that V4 may prove to be a more suitable locus of cortical visual prosthesis implantation.
Modeling and Analysis Methods:
Activation (eg. BOLD task-fMRI) 2
Univariate Modeling
Perception, Attention and Motor Behavior:
Perception: Visual 1
Keywords:
FUNCTIONAL MRI
Perception
Vision
1|2Indicates the priority used for review
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Please indicate below if your study was a "resting state" or "task-activation” study.
Task-activation
Healthy subjects only or patients (note that patient studies may also involve healthy subjects):
Healthy subjects
Was this research conducted in the United States?
No
Were any human subjects research approved by the relevant Institutional Review Board or ethics panel?
NOTE: Any human subjects studies without IRB approval will be automatically rejected.
Yes
Were any animal research approved by the relevant IACUC or other animal research panel?
NOTE: Any animal studies without IACUC approval will be automatically rejected.
Not applicable
Please indicate which methods were used in your research:
Functional MRI
Structural MRI
Behavior
For human MRI, what field strength scanner do you use?
3.0T
Which processing packages did you use for your study?
SPM
Provide references using APA citation style.
Torfs, K., Panis, S., & Wagemans, J. (2010). Identification of fragmented object outlines: A dynamic interplay between different component processes. Visual Cognition, 18(8), 1133–1164. https://doi.org/10.1080/13506281003693593
No