GABA, noise and gain in human visual cortex.

High levels of GABA (gamma-aminobutyric acid, the brain's primary inhibitory neurotransmitter) are associated with enhanced cognitive and perceptual performance. It has been proposed that these effects result from GABA reducing neural noise or variability, but the precise mechanisms remain unknown. We have measured how individual differences in GABA concentration in the visual cortex are related to performance on a visual contrast discrimination task.

Brightening and Dimming Aftereffects at Low and High Luminance.

Adaptation to a spatially uniform field that increases or decreases in luminance over time yields a "ramp aftereffect", whereby a steady, uniform luminance appears to dim or brighten, and an appropriate non-uniform test field appears to move. We measured the duration of this aftereffect of adaptation to ascending and descending luminance for a wide range of temporal frequencies and luminance amplitudes. Three types of luminance ramp profiles were used: linear, logarithmic, and exponential.

Systematic review of recent guidelines for pharmacological treatments of bipolar disorders in adults.

Background: To examine the similarities and differences among practice guidelines for managing bipolar disorders (BDs) in adults.

Methods: A literature search in PubMed/Medline was performed using multiple search terms and bibliographies for guidelines from July 2013 (since FDA approval of lurasidone) to June 2017.

Results: Six treatment guidelines for BDs in adults were identified.

GABA predicts visual intelligence.

Early psychological researchers proposed a link between intelligence and low-level perceptual performance. It was recently suggested that this link is driven by individual variations in the ability to suppress irrelevant information, evidenced by the observation of strong correlations between perceptual surround suppression and cognitive performance. However, the neural mechanisms underlying such a link remain unclear.

Perceived speed in peripheral vision can go up or down.

We measured the perceived speed and contrast of patterns in peripheral vision relative to foveal patterns for a range of eccentricities at both mesopic and photopic levels. The results indicate that perceived speed varies with eccentricity, speed, and luminance. At high (photopic) luminance, patterns appear slower when viewed peripherally rather than foveally, but at low (mesopic) luminance fast-moving patterns can appear faster when viewed peripherally.

Perceptual biases are inconsistent with Bayesian encoding of speed in the human visual system.

The notion that Bayesian processes are fundamental to brain function and sensory processing has recently received much support, and a number of Bayesian accounts of how the brain encodes the speed of moving objects have been proposed that challenge earlier mechanistic models. We measured the perceived speed of low contrast patterns at both low (2.5 cd m(-2)) and high (25 cd m(-2)) luminance in order to assess these competing models of how the human visual system encodes speed.

Implicit representations of luminance and the temporal structure of moving stimuli in multiple regions of human visual cortex revealed by multivariate pattern classification analysis.

The generation of a behaviorally relevant cue to the speed of objects around us is critical to our ability to navigate safely within our environment. However, our perception of speed is often distorted by prevailing conditions. For instance, as luminance is reduced, our perception of the speed of fast-moving patterns can be increased by as much as 30%.

The effect of contrast on perceived speed and flicker.

Slowly moving low contrast patterns appear to drift more slowly than higher contrast patterns. It has been reported that this effect of contrast is reversed for flickering patterns such that they appear to flicker faster than high contrast patterns. This apparent difference in the effect of contrast on perceived speed and flicker may place important constraints upon models of speed encoding in the human visual system.

The effect of luminance on simulated driving speed.

Perceived speed is modulated by a range of stimulus attributes such as contrast, luminance and adaptation duration. It has been suggested that such changes in perceived speed may influence driving behaviour. In order to evaluate the effect of luminance on driving speed we have measured subjects' driving speed in a driving simulator for a range of luminance and speed over time.

Dietary supplementation of creatine monohydrate reduces the human fMRI BOLD signal.

Creatine monohydrate is an organic acid that plays a key role in ATP re-synthesis. Creatine levels in the human brain vary considerably and dietary supplementation has been found to enhance cognitive performance in healthy individuals. To explore the possibility that the fMRI Blood Oxygen Level Dependent (BOLD) response is influenced by creatine levels, BOLD responses to visual stimuli were measured in visual cortex before and after a week of creatine administration in healthy human volunteers.

Perceived direction of plaid motion is not predicted by component speeds.

It has been shown that the perceived direction of a plaid with components of unequal contrast is biased towards the direction of the higher-contrast component [Stone, L. S., Watson, A.

Perceptual distortions of speed at low luminance: evidence inconsistent with a Bayesian account of speed encoding.

Our perception of speed has been shown to be distorted under a number of viewing conditions. Recently the well-known reduction of perceived speed at low contrast has led to Bayesian models of speed perception that account for these distortions with a slow speed 'prior'. To test the predictive, rather than the descriptive, power of the Bayesian approach we have investigated perceived speed at low luminance.

A ratio model of perceived speed in the human visual system.

The perceived speed of moving images changes over time. Prolonged viewing of a pattern (adaptation) leads to an exponential decrease in its perceived speed. Similarly, responses of neurones tuned to motion reduce exponentially over time.

Speed can go up as well as down at low contrast: implications for models of motion perception.

It is well-known that reducing the contrast of a slow moving stimulus reduces its apparent speed. [Thompson, P. (1982).

Motion, flash, and flicker: a unified spatiotemporal model of perceived edge sharpening.

Blurred edges appear sharper in motion than when they are stationary. We proposed a model of this motion sharpening that invokes a local, nonlinear contrast transducer function (Hammett et al, 1998 Vision Research 38 2099-2108). Response saturation in the transducer compresses or 'clips' the input spatial waveform, rendering the edges as sharper.

Motion sharpening and contrast: gain control precedes compressive non-linearity?

Blurred edges appear sharper in motion than when they are stationary. We (Vision Research 38 (1998) 2108) have previously shown how such distortions in perceived edge blur may be accounted for by a model which assumes that luminance contrast is encoded by a local contrast transducer whose response becomes progressively more compressive as speed increases. If the form of the transducer is fixed (independent of contrast) for a given speed, then a strong prediction of the model is that motion sharpening should increase with increasing contrast.

Seeing blur: 'motion sharpening' without motion.

It is widely supposed that things tend to look blurred when they are moving fast. Previous work has shown that this is true for sharp edges but, paradoxically, blurred edges look sharper when they are moving than when stationary. This is 'motion sharpening'.