Biology subjects

Tuten, W. S.

Publications and source records attributed to Tuten, W. S..

5 recordsLinked to original sources

bioRxiv2025

Local variations in L/M ratio influence the detection and color naming of small spots

The distribution of long (L), middle (M), and short (S) wavelength sensitive cones in the retina determines how different frequencies of incident light are sampled across space and has been hypothesized to influence spatial and color vision. We examined how the detection and color naming of small, short-duration increment stimuli ({lambda} = 543 or 680 nm) depend on the local spectral topography of the cone mosaic. Stimuli were corrected for optical aberrations by an adaptive optics system and targeted to locations in the parafovea where cone spectral types were known. We found that sensitivity to 680 nm light, normalized by sensitivity to 543 nm light, grew with the proportion of L cones at the stimulated locus, though intra- and intersubject variability was considerable. A similar trend was derived from a simple model of the achromatic (L+M) pathway suggesting that small spot detection mainly relies on a non-opponent mechanism. Most stimuli were called achromatic, with red and green responses becoming more common as stimulus intensity increased and as the local L/M ratio became more symmetric. The proximity of S cones to the stimulated region did not influence the likelihood of eliciting a chromatic percept. Our detection data confirm earlier reports that small spot psychophysics can reveal information about local cone topography, and our color naming findings suggest that chromatic sensitivity may improve when the L/M ratio approaches unity.

neuroscience↗

bioRxiv2022

It's not easy seeing green: the veridical perception of small spots

When single cones are stimulated with spots of 543-nm light presented against a white background, subjects report percepts that vary between predominately red, white, and green. However, light of the same spectral composition viewed over a large field under normal viewing conditions looks invariably green and highly saturated. It remains unknown what stimulus parameters are most important for governing the color appearance in the transition between these two extreme cases. The current study varied the size, intensity and retinal motion of stimuli presented in an adaptive optics scanning laser ophthalmoscope. Stimuli were either stabilized on target locations or allowed to drift across the retina with the eyes natural motion. Increasing both stimulus size and intensity led to higher likelihoods that monochromatic spots of light were perceived as green, while only higher intensities led to increases in perceived saturation. The data also show an interaction between size and intensity, suggesting that the balance between magnocellular and parvocellular activation may be critical factors for color perception. Surprisingly, under the range of conditions tested, color appearance did not depend on whether stimuli were stabilized or not. Sequential activation of many cones does not appear to drive hue and saturation perception as effectively as simultaneous activation of many cones.

neuroscience↗

bioRxiv2019

Spatial summation of individual cones in human color vision

The human retina contains three classes of cone photoreceptors each sensitive to different portions of the visual spectrum: long (L), medium (M) and short (S) wavelengths. Color information is computed by downstream neurons that compare relative activity across the three cone types. How cone signals are combined at a cellular scale has been more difficult to resolve. This is especially true near the fovea, where spectrally-opponent neurons in the parvocellular pathway draw excitatory input from a single cone and thus even the smallest stimulus will engage multiple color-signaling neurons. We used an adaptive optics microstimulator to target individual and pairs of cones with light. Consistent with prior work, we found that color percepts elicited from individual cones were predicted by their spectral sensitivity, although there was considerable variability even between cones within the same spectral class. The appearance of spots targeted at two cones were predicted by an average of their individual activations. However, two cones of the same subclass elicited percepts that were systematically more saturated than predicted by an average. Together, these observations suggest both spectral opponency and prior experience influence the appearance of small spots.

neuroscience↗

bioRxiv2018

Spatial summation in the human fovea: the effect of optical aberrations and fixational eye movements

Psychophysical inferences about the neural mechanisms supporting spatial vision can be undermined by uncertainties introduced by optical aberrations and fixational eye movements, particularly in fovea where the neuronal grain of the visual system is fine. We examined the effect of these pre-neural factors on photopic spatial summation in the human fovea using a custom adaptive optics scanning light ophthalmoscope that provided control over optical aberrations and retinal stimulus motion. Consistent with previous results, Riccos area of complete summation encompassed multiple photoreceptors when measured with ordinary amounts of ocular aberrations and retinal stimulus motion. When both factors were minimized experimentally, summation areas were essentially unchanged, suggesting that foveal spatial summation is limited by post-receptoral neural pooling. We compared our behavioral data to predictions generated with a physiologically-inspired front-end model of the visual system, and were able to capture the shape of the summation curves obtained with and without pre-retinal factors using a single post-receptoral summing filter of fixed spatial extent. Given our data and modeling, neurons in the magnocellular visual pathway, such as parasol ganglion cells, provide a candidate neural correlate of Riccos area in the central fovea.

neuroscience↗

bioRxiv2018

Sensations from a single M-cone depend on the activity of surrounding S-cones

Color vision requires the activity of cone photoreceptors to be compared in post-receptoral circuitry. Decades of psychophysical measurements have quantified the nature of these comparative interactions on a coarse scale. How such findings generalize to a cellular scale remains unclear. To answer that question, we quantified the influence of surrounding light on the appearance of spots targeted to individual cones. The eyes aberrations were corrected with adaptive optics and retinal position was precisely tracked in real-time to compensate for natural movement. Subjects reported the color appearance of each spot. A majority of L-and M-cones consistently gave rise to the sensation of white, while a smaller group repeatedly elicited hue sensations. When blue sensations were reported they were more likely mediated by M- than L-cones. Blue sensations were elicited from M-cones against a short-wavelength light that preferentially elevated the quantal catch in surrounding S-cones, while stimulation of the same cones against a white background elicited green sensations. In one of two subjects, proximity to S-cones increased the probability of blue reports when M-cones were probed. We propose that M-cone increments excited both green and blue opponent pathways, but the relative activity of neighboring cones favored one pathway over the other.

neuroscience↗