Biology subjects

Bowers, N. R.

Publications and source records attributed to Bowers, N. R..

4 recordsLinked to original sources

bioRxiv2025

The Optimal Retinal Locus for High-Resolution Vision in Space and Time

Humans exhibit machine-like eye-movement behavior in space and time while performing challenging visual resolution tasks. Fewer microsaccades occur as stimulus presentation is imminent. Drifts and microsaccades combine to confine the landing location of an anticipated visual stimulus to a tiny retinal region: the preferred retinal locus (PRL). We find that this location confers the best visual acuity despite it being offset from the anatomical fovea (the location of maximum cone density). We also find that acuity is best when the last microsaccade occurs 400msec or longer before stimulus presentation. The machine-like eye movements are involuntary and not perceived. Our findings thus reveal a highly evolved oculomotor system such that gaze direction during fixation is rarely far enough from the PRL to cause a decline in visual resolution. TeaserHumans exhibit machine-like eye-movement behavior during fine visual tasks that rarely deviates from an optimal retinal location.

neuroscience↗

bioRxiv2025

Chromatic and Achromatic Contrast Sensitivity in the far Periphery

The contrast sensitivity function (CSF) has been studied extensively since the 1960s, however most studies to date have focused on the central region of the visual field. The current study aims to address two gaps in previous measurements: First, it provides a detailed measurement of the CSF for achromatic and, importantly, also chromatic stimuli in the far periphery of up to 90 degrees of visual angle. Second, we describe visual sensitivity around the monocular/binocular boundary that is naturally present in the far periphery. In the first experiment, the CSF was measured in 3 different conditions: Stimuli were either Achromatic (L+M), Red-Green (L-M) or and Yellow-Violet (S-(L+M)) gabor patches. Overall, results followed the expected patterns established in the near periphery, but achromatic sensitivity in the far periphery was mostly under-estimated by current models of visual perception, the quick decay in sensitivity observed for red-green stimuli slows down in the periphery. The decay of sensitivity for yellow-violett stimuli roughly matches the decay for achromatic stimuli even up to the far periphery. For the second experiment, we compared binocular and monocular visual sensitivity at different locations in the visual field. We observed a consistent increase of visual sensitivity for binocular viewing in the central part of the visual field compared to monocular viewing, but this benefit already decreased within the binocular visual field in the periphery. Together, these data provide a detailed description of visual sensitivity in the far periphery. These measurements can help to improve current models of visual sensitivity and can be vital for applications in full-field visual displays in virtual and augmented reality.

neuroscience↗

bioRxiv2021

Fixational Eye Movements Depend on Task and Target

Human fixational eye movements are so small and precise that they require high-speed, accurate tools to fully reveal their properties and functional roles. Where the fixated image lands on the retina and how it moves for different levels of visually demanding tasks is the subject of the current study. An Adaptive Optics Scanning Laser Ophthalmoscope (AOSLO) was used to image, track and present Maltese cross, disk, concentric circles, Vernier and tumbling-E letter fixation targets to healthy subjects. During these different passive (static) or active (discriminating) fixation tasks under natural eye motion, the landing position of the target on the retina was tracked in space and time over the retinal image directly. We computed both the eye motion and the exact trajectory of the fixated targets motion over the retina. We confirmed that compared to passive fixation, active tasks elicited a partial inhibition of microsaccades, leading to longer drifts periods compensated by larger corrective saccades. Consequently the fixation stability during active tasks was larger overall than during passive tasks. The preferred retinal locus of fixation was the same for each task and did not coincide with the location of the peak cone density.

neuroscience↗

bioRxiv2018

The effects of fixational tremor on the retinal image

The study of fixational eye motion (FEM) has implications for the neural and computational underpinnings of vision. One component of FEM is tremor, a high-frequency oscillatory jitter reported to be anywhere from [~]5 to 60 seconds of arc in amplitude. In order to isolate the effects of tremor on the retinal image directly and in the absence of optical blur, high-frequency, high-resolution eye traces were collected in 6 subjects from videos recorded with an Adaptive Optics Scanning Laser Ophthalmoscope. Videos were acquired while subjects engaged in an active fixation task where they fixated on a tumbling E stimulus and reported changes in its orientation. Spectral analysis was conducted on isolated segments of optical drift. The resultant amplitude spectra showed a slight deviation from the traditional 1/f nature of optical drift in the frequency range of 50-100 Hz, which is indicative of tremor; however, the amplitude of this deviation rarely exceeded one second of arc, smaller than any magnitude previously reported.

neuroscience↗