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. 2021 Jul:184:23-29.
doi: 10.1016/j.visres.2021.02.009. Epub 2021 Mar 26.

Glow in the dark: Using a heat-sensitive camera for blind individuals with prosthetic vision

Roksana Sadeghi  1 , Arathy Kartha  2 , Michael P Barry  3 , Chris Bradley  2 , Paul Gibson  4 , Avi Caspi  5 , Arup Roy  3 , Gislin Dagnelie  2
Affiliations

Glow in the dark: Using a heat-sensitive camera for blind individuals with prosthetic vision

Roksana Sadeghi et al. Vision Res. 2021 Jul.

Abstract

To date, retinal implants are the only available treatment for blind individuals with retinal degenerations such as retinitis pigmentosa. Argus II is the only visual implant with FDA approval, with more than 300 users worldwide. Argus II stimulation is based on a grayscale image coming from a head-mounted visible-light camera. Normally, the 11°×19° field of view of the Argus II user is full of objects that may elicit similar phosphenes. The prosthesis cannot meaningfully convey so much visual information, and the percept is reduced to an ambiguous impression of light. This study is aimed at investigating the efficacy of simplifying the video input in real-time using a heat-sensitive camera. Data were acquired from four Argus II users in 5 stationary tasks with either hot objects or human targets as stimuli. All tasks were of m-alternative forced choice design where precisely one of the m≥2 response alternatives was defined to be "correct" by the experimenter. To compare performance with heat-sensitive and normal cameras across all tasks, regardless of m, we used an extension of signal detection theory to latent variables, estimating person ability and item difficulty in d' units. Results demonstrate that subject performance was significantly better across all tasks with the thermal camera compared to the regular Argus II camera. The future addition of thermal imaging to devices with very poor spatial resolution may have significant real-life benefits for orientation, personal safety, and social interactions, thereby improving quality of life.

Keywords: Activities of daily living; M-alternative forced choice; Performance measures; Psychophysics; Retinal implant; Thermal camera.

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Figures

Fig. 1.
Fig. 1.
Side-by-side views of the external Argus II system components and the heat-sensitive adaptation. A) A miniature head-mounted video camera sends a grayscale image to the VPU, and the VPU transfers energy and the real-time stimulation parameters to the implant array through the transmitter coil. B) Heat-sensitive camera connected to the electronics box that processes and transfers the thermal camera images to the VPU for transmission to the implant through the external transmitter coil.
Fig. 2.
Fig. 2.
Image frame examples A) from a visible-light camera and B) a thermal camera. Approximation of Argus II user percept from the image frame example with C) visible-light camera and D) a thermal camera.
Fig. 3.
Fig. 3.
Subjects’ view for tasks 4 and 5 is indicated by the white rectangle, which approximates the visual field of an Argus II user.
Fig. 4.
Fig. 4.
Estimated item measures in d′ units show the range of difficulty levels for the tasks in our experiment. Error bars specify 95% confidence intervals.
Fig. 5.
Fig. 5.
Estimated person measures for each subject across all tasks, relative to the average person measure (at d′ = 0) across all tasks, are plotted for the heat-sensitive camera (red squares) and visible-light camera (blue circles). Higher person measures indicate more capable persons. The error bars show the estimated standard errors.
Fig. 6.
Fig. 6.
Estimated person measures across subjects, by task, relative to the average person ability (d′ = 0), for the thermal (red squares) and visible-light (blue circles) cameras. Vertical lines separating the tasks are for emphasis that each task has its own performance average. Error bars show the estimated standard errors.
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