Optical stimulation of inferior temporal cortex induces object-speci�c visual distortions.

: 9 To be able to effectively restore vision by direct cortical stimulation, we need to 10 understand the perceptual events induced by stimulation of high-level visual cortices. We trained 11 macaque monkeys to detect and report optogenetic impulses delivered to their inferior temporal 12 cortices. In a series of experiments, we observed that detection of cortical stimulation highly 13 depends on the choice of images presented to the eyes and that detection of cortical stimulation is 14 most difficult when the animal fixates on a blank screen. We show that local stimulation of 15 object selective parts of the visual cortex induce perceptual events that are easy to detect as 16 object-dependent distortions of the concurrent contents of vision. These findings invite 17 expanding the scope of visual prosthetics beyond the primary visual cortex. 18 19 20 21 22 23 24


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Main Text: 28 Perturbation of neural activity in the visual system alters visual perception (Brindley &  that is suggestive of face-specific distortions, but can be explained by face hallucinations as well 79 because a hallucinatory face may interact with the match-to-sample task more for faces than the 80 other stimuli. While these studies reveal specific perceptual changes resulting from artificial 81 perturbation of the neural activity, they remain mostly agnostic with respect to the hallucinatory 82 versus distortive nature of those changes.

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In this study, we designed a novel psychophysical task to systematically investigate the  cortex while fixating at images of various objects and scenes (Figure 1.b). In each trial, following 97 fixation, an image was displayed on the screen for 1 s. In half of the trials, randomly selected, a 98 200 ms illumination impulse was delivered to IT cortex halfway through the image presentation, 99 and the animal was rewarded for correctly identifying whether the trial did or did not contain 100 cortical stimulation. The image content was independent of whether brain stimulation would or 101 would not occur and the subjects' exclusive behavioral task was to detect if brain stimulation 102 occurred in a given trial. We found this approach produced robust and large behavioral effects.    Figure S1.a). In the stimulation trials (50% of trials), we randomly interleaved 134 stimulations of two cortical sites (~3 mm apart). We found that the performance in detection of 135 cortical illumination systematically varies while the animals fixate at different images, creating a 136 unique array of performances for each cortical position that we refer to as the 'detection profile'.
137 Figure 2.a shows a detection profile for one stimulation site in monkey Ph (see Figure S2 for   crowding effect) with screen images (Toet & Levi, 1992). However, performance for the "no    Array at the beginning of each trial and trial delivery was paused if the temperature on the LED 285 die rose more than 3° C above the baseline temperature, and restarted once they were less than 1° 286 C above the baseline. 3° C at the LED die translates to approximately 0.5° C temperature change 287 on the cortical surface; this temperature management regime is detailed in Rajalingham et al.       Figure S3). Where i is the trial number. x is illumination power, α, β, β1, …, βn are the fit coefficients. 425 For each trial, the λ that matches the image index is assigned 1, and the rest are assigned 0.   Competing interests: 571 The authors declare that there is no conflict of interest.

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Data and material availability: 573 The data and material that support the findings of this study are available on request from the 574 corresponding author R.A.  were only shown to monkey Sp. "Image" 35 was the "no image" condition and the "no image" 645 text did not appear in the experiment. b) Images used during the training phase for each monkey.

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The last row of images for each monkey were displayed at 30°x30°. c) Image stimulus used in 647 Experiment 3 for each monkey. All images were displayed at 8°x8°.