245 research outputs found
Purification and properties of adenosine triphosphatase from Chromatium vinosum chromatophores
Optimal measurement of visual motion across spatial and temporal scales
Sensory systems use limited resources to mediate the perception of a great
variety of objects and events. Here a normative framework is presented for
exploring how the problem of efficient allocation of resources can be solved in
visual perception. Starting with a basic property of every measurement,
captured by Gabor's uncertainty relation about the location and frequency
content of signals, prescriptions are developed for optimal allocation of
sensors for reliable perception of visual motion. This study reveals that a
large-scale characteristic of human vision (the spatiotemporal contrast
sensitivity function) is similar to the optimal prescription, and it suggests
that some previously puzzling phenomena of visual sensitivity, adaptation, and
perceptual organization have simple principled explanations.Comment: 28 pages, 10 figures, 2 appendices; in press in Favorskaya MN and
Jain LC (Eds), Computer Vision in Advanced Control Systems using Conventional
and Intelligent Paradigms, Intelligent Systems Reference Library,
Springer-Verlag, Berli
Neural wave interference in inhibition-stabilized networks
We study how excitation propagates in chains of inhibition-stabilized neural networks with nearest-neighbor coupling. The excitation generated by local stimuli in such networks propagates across space and time, forming spatiotemporal waves that affect the dynamics of excitation generated by stimuli separated spatially and temporally. These interactions form characteristic interference patterns, manifested as network preferences: for spatial and temporal frequencies of stimulus intensity, for stimulus velocities, and as contextual ("lateral") interactions between stimuli. Such preferences have been previously attributed to distinct specialized mechanisms
Mechanisms of spatiotemporal selectivity in cortical area MT
Cortical sensory neurons are characterized by selectivity to stimulation. This selectivity was
originally viewed as a part of the fundamental “receptive field” characteristic of neurons. This view
was later challenged by evidence that receptive fields are modulated by stimuli outside of the
classical receptive field. Here we show that even this modified view of selectivity needs revision.
We measured spatial frequency selectivity of neurons in cortical area MT of alert monkeys and
found that their selectivity strongly depends on luminance contrast, shifting to higher spatial
frequencies as contrast increases. The changes of preferred spatial frequency are large at low
temporal frequency and they decrease monotonically as temporal frequency increases. That is,
even interactions among basic stimulus dimensions of luminance contrast, spatial frequency and
temporal frequency strongly influence neuronal selectivity. This dynamic nature of neuronal
selectivity is inconsistent with the notion of stimulus preference as a stable characteristic of
cortical neurons
Effects of Elsholtzia splendens and Cirsium japonicum on premenstrual syndrome
Premenstrual syndrome is a common chronic disorder in most women of reproductive age. The main symptoms are depression, anxiety, tension, feeling out of control, and mastalgia. In premenstrual syndrome, the effects of aromatic edible Elsholtzia splendens and Cirsium japonicum were investigated for over 3 months in 30 women participants in their twenties. In the Elsholtzia splendens capsule treated group, scores of depression and anxiety were significantly lower than those in the Cirsium japonicum capsule treated group. Moreover, instability of the premenstrual assessment form was significantly decreased in the Elsholtzia splendens capsule treated group. Our results suggest that Elsholtzia splendens could be an effective plant material in relieving symptoms of premenstrual syndrome
Interaction of perceptual grouping and crossmodal temporal capture in tactile apparent-motion
Previous studies have shown that in tasks requiring participants to report the direction of apparent motion, task-irrelevant mono-beeps can "capture'' visual motion perception when the beeps occur temporally close to the visual stimuli. However, the contributions of the relative timing of multimodal events and the event structure, modulating uni- and/or crossmodal perceptual grouping, remain unclear. To examine this question and extend the investigation to the tactile modality, the current experiments presented tactile two-tap apparent-motion streams, with an SOA of 400 ms between successive, left-/right-hand middle-finger taps, accompanied by task-irrelevant, non-spatial auditory stimuli. The streams were shown for 90 seconds, and participants' task was to continuously report the perceived (left-or rightward) direction of tactile motion. In Experiment 1, each tactile stimulus was paired with an auditory beep, though odd-numbered taps were paired with an asynchronous beep, with audiotactile SOAs ranging from -75 ms to 75 ms. Perceived direction of tactile motion varied systematically with audiotactile SOA, indicative of a temporal-capture effect. In Experiment 2, two audiotactile SOAs-one short (75 ms), one long (325 ms)-were compared. The long-SOA condition preserved the crossmodal event structure (so the temporal-capture dynamics should have been similar to that in Experiment 1), but both beeps now occurred temporally close to the taps on one side (even-numbered taps). The two SOAs were found to produce opposite modulations of apparent motion, indicative of an influence of crossmodal grouping. In Experiment 3, only odd-numbered, but not even-numbered, taps were paired with auditory beeps. This abolished the temporal-capture effect and, instead, a dominant percept of apparent motion from the audiotactile side to the tactile-only side was observed independently of the SOA variation. These findings suggest that asymmetric crossmodal grouping leads to an attentional modulation of apparent motion, which inhibits crossmodal temporal-capture effects
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