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Simulation of thalamic prosthetic vision: reading accuracy, speed, and acuity in sighted humans.

Vurro M, Crowell AM, Pezaris JS - Front Hum Neurosci (2014)

Bottom Line: Reading accuracy, reading speed, and reading acuity of 20 subjects were measured as a function of letter size, using a task based on the MNREAD chart.Results here were consistent with previous results from our laboratory.Results were also consistent with those from the literature, despite using naive subjects who were not trained on the simulator, in contrast to other reports.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurosurgery, Massachusetts General Hospital/Harvard Medical School Boston, MA, USA.

ABSTRACT
The psychophysics of reading with artificial sight has received increasing attention as visual prostheses are becoming a real possibility to restore useful function to the blind through the coarse, pseudo-pixelized vision they generate. Studies to date have focused on simulating retinal and cortical prostheses; here we extend that work to report on thalamic designs. This study examined the reading performance of normally sighted human subjects using a simulation of three thalamic visual prostheses that varied in phosphene count, to help understand the level of functional ability afforded by thalamic designs in a task of daily living. Reading accuracy, reading speed, and reading acuity of 20 subjects were measured as a function of letter size, using a task based on the MNREAD chart. Results showed that fluid reading was feasible with appropriate combinations of letter size and phosphene count, and performance degraded smoothly as font size was decreased, with an approximate doubling of phosphene count resulting in an increase of 0.2 logMAR in acuity. Results here were consistent with previous results from our laboratory. Results were also consistent with those from the literature, despite using naive subjects who were not trained on the simulator, in contrast to other reports.

No MeSH data available.


Related in: MedlinePlus

Phases of the experimental task. One trial of the task is shown in a sequence of snapshots. The task had four distinct phases, Start, Pre-Stimulus, Reading, and End, with the bulk of the time spent in the Reading phase. Green-blue dots indicate the initial central fixation point used to engage the trial, and the subsequent dot at the center top used to advance to the next trial. Red crosses indicate the instantaneous gaze position, and red arrows, the gaze motion from one snapshot to the next (neither would appear to the subject). During the Reading phase, the subject is free to look about the screen, but gaze patterns typically followed the three lines of text with a series of fixations on each line. The (simulated) subject in this instance can be seen to read across each of the three lines, left to right and top to bottom, before looking to the trigger point in the End phase. The image in the center panel corresponds to the image in Figure 3.
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Figure 5: Phases of the experimental task. One trial of the task is shown in a sequence of snapshots. The task had four distinct phases, Start, Pre-Stimulus, Reading, and End, with the bulk of the time spent in the Reading phase. Green-blue dots indicate the initial central fixation point used to engage the trial, and the subsequent dot at the center top used to advance to the next trial. Red crosses indicate the instantaneous gaze position, and red arrows, the gaze motion from one snapshot to the next (neither would appear to the subject). During the Reading phase, the subject is free to look about the screen, but gaze patterns typically followed the three lines of text with a series of fixations on each line. The (simulated) subject in this instance can be seen to read across each of the three lines, left to right and top to bottom, before looking to the trigger point in the End phase. The image in the center panel corresponds to the image in Figure 3.

Mentions: The experiment consisted of a single block of 48 trials. Each trial in the block was subdivided into a series of four phases, Start, Pre-Stimulus, Reading, and End (see Figure 5). During the Start Phase, a fixation point appeared in the middle of the screen that the subject was required to foveate in order to engage the experiment. Once foveated for the duration of the Pre-Stimulus phase, the fixation point was extinguished. The Reading phase then followed with one of the sentences displayed along with an additional dot near the top center of the screen. The subject was required to read the sentence out loud, as quickly and accurately as possible, or to declare their inability to read it. In order to advance to the next sentence, subjects looked at the top center dot. Subjects could take as long as they wanted, consistent with reading quickly and accurately. Once the subject foveated the top center dot for 350 ms, the trial entered the End Phase, the screen was blanked, and a 2000 ms pause provided an intertrial interval before the next trial commenced. An audio recording was made for the entirety of each experiment.


Simulation of thalamic prosthetic vision: reading accuracy, speed, and acuity in sighted humans.

Vurro M, Crowell AM, Pezaris JS - Front Hum Neurosci (2014)

Phases of the experimental task. One trial of the task is shown in a sequence of snapshots. The task had four distinct phases, Start, Pre-Stimulus, Reading, and End, with the bulk of the time spent in the Reading phase. Green-blue dots indicate the initial central fixation point used to engage the trial, and the subsequent dot at the center top used to advance to the next trial. Red crosses indicate the instantaneous gaze position, and red arrows, the gaze motion from one snapshot to the next (neither would appear to the subject). During the Reading phase, the subject is free to look about the screen, but gaze patterns typically followed the three lines of text with a series of fixations on each line. The (simulated) subject in this instance can be seen to read across each of the three lines, left to right and top to bottom, before looking to the trigger point in the End phase. The image in the center panel corresponds to the image in Figure 3.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4219440&req=5

Figure 5: Phases of the experimental task. One trial of the task is shown in a sequence of snapshots. The task had four distinct phases, Start, Pre-Stimulus, Reading, and End, with the bulk of the time spent in the Reading phase. Green-blue dots indicate the initial central fixation point used to engage the trial, and the subsequent dot at the center top used to advance to the next trial. Red crosses indicate the instantaneous gaze position, and red arrows, the gaze motion from one snapshot to the next (neither would appear to the subject). During the Reading phase, the subject is free to look about the screen, but gaze patterns typically followed the three lines of text with a series of fixations on each line. The (simulated) subject in this instance can be seen to read across each of the three lines, left to right and top to bottom, before looking to the trigger point in the End phase. The image in the center panel corresponds to the image in Figure 3.
Mentions: The experiment consisted of a single block of 48 trials. Each trial in the block was subdivided into a series of four phases, Start, Pre-Stimulus, Reading, and End (see Figure 5). During the Start Phase, a fixation point appeared in the middle of the screen that the subject was required to foveate in order to engage the experiment. Once foveated for the duration of the Pre-Stimulus phase, the fixation point was extinguished. The Reading phase then followed with one of the sentences displayed along with an additional dot near the top center of the screen. The subject was required to read the sentence out loud, as quickly and accurately as possible, or to declare their inability to read it. In order to advance to the next sentence, subjects looked at the top center dot. Subjects could take as long as they wanted, consistent with reading quickly and accurately. Once the subject foveated the top center dot for 350 ms, the trial entered the End Phase, the screen was blanked, and a 2000 ms pause provided an intertrial interval before the next trial commenced. An audio recording was made for the entirety of each experiment.

Bottom Line: Reading accuracy, reading speed, and reading acuity of 20 subjects were measured as a function of letter size, using a task based on the MNREAD chart.Results here were consistent with previous results from our laboratory.Results were also consistent with those from the literature, despite using naive subjects who were not trained on the simulator, in contrast to other reports.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurosurgery, Massachusetts General Hospital/Harvard Medical School Boston, MA, USA.

ABSTRACT
The psychophysics of reading with artificial sight has received increasing attention as visual prostheses are becoming a real possibility to restore useful function to the blind through the coarse, pseudo-pixelized vision they generate. Studies to date have focused on simulating retinal and cortical prostheses; here we extend that work to report on thalamic designs. This study examined the reading performance of normally sighted human subjects using a simulation of three thalamic visual prostheses that varied in phosphene count, to help understand the level of functional ability afforded by thalamic designs in a task of daily living. Reading accuracy, reading speed, and reading acuity of 20 subjects were measured as a function of letter size, using a task based on the MNREAD chart. Results showed that fluid reading was feasible with appropriate combinations of letter size and phosphene count, and performance degraded smoothly as font size was decreased, with an approximate doubling of phosphene count resulting in an increase of 0.2 logMAR in acuity. Results here were consistent with previous results from our laboratory. Results were also consistent with those from the literature, despite using naive subjects who were not trained on the simulator, in contrast to other reports.

No MeSH data available.


Related in: MedlinePlus