Postural responses to sinusoidal modulations of viewpoint position in a virtual environment.

Visual self-motion information is known to contribute to postural control, but it is unclear precisely which aspects of visual motion information drive changes in posture. We report here results for standing humans which suggest that there is a speed of movement threshold that must be exceeded by a visual stimulus if a posture response is to be generated. We use signal-to-noise ratio (SNR) methods to measure the strength of steady-state visually evoked posture responses (SSVEPRs) to sinusoidal modulations of visual viewpoint position in a virtual environment (VE).

Tracking feature-based attention.

Objective: Feature-based attention (FBA) helps one detect objects with a particular color, motion, or orientation. FBA works globally; the attended feature is enhanced at all positions in the visual field. This global property of FBA lets one use stimuli presented in the peripheral visual field to track attention in a task presented centrally.

Effects of unexpected visual motion on postural sway and motion sickness.

Motion sickness is thought to occur when the brain's assumptions about incoming sensory information do not match the actual signals received. These signals must involve the vestibular system for motion sickness to occur. In this paper, we describe an experiment in which subjects experienced unexpected visual motions, or perturbations, as they navigated a virtual environment (VE) while standing and wearing a head mounted display (HMD) or while viewing a monitor.

Cybersickness without the wobble: Experimental results speak against postural instability theory.

It has been suggested that postural instability is necessary for cybersickness to occur. Seated and standing subjects used a head-mounted display to view a virtual tunnel that rotated about their line of sight. We found that the offset direction of perceived vertical settings matched the direction of the tunnel's rotation, so replicating earlier findings.

Attention selectively modulates cortical entrainment in different regions of the speech spectrum.

Recent studies have uncovered a neural response that appears to track the envelope of speech, and have shown that this tracking process is mediated by attention. It has been argued that this tracking reflects a process of phase-locking to the fluctuations of stimulus energy, ensuring that this energy arrives during periods of high neuronal excitability. Because all acoustic stimuli are decomposed into spectral channels at the cochlea, and this spectral decomposition is maintained along the ascending auditory pathway and into auditory cortex, we hypothesized that the overall stimulus envelope is not as relevant to cortical processing as the individual frequency channels; attention may be mediating envelope tracking differentially across these spectral channels.

Envelope responses in single-trial EEG indicate attended speaker in a 'cocktail party'.

Objective: Recent studies have shown that auditory cortex better encodes the envelope of attended speech than that of unattended speech during multi-speaker ('cocktail party') situations. We investigated whether these differences were sufficiently robust within single-trial electroencephalographic (EEG) data to accurately determine where subjects attended. Additionally, we compared this measure to other established EEG markers of attention.

Suppression of competing speech through entrainment of cortical oscillations.

People are highly skilled at attending to one speaker in the presence of competitors, but the neural mechanisms supporting this remain unclear. Recent studies have argued that the auditory system enhances the gain of a speech stream relative to competitors by entraining (or "phase-locking") to the rhythmic structure in its acoustic envelope, thus ensuring that syllables arrive during periods of high neuronal excitability. We hypothesized that such a mechanism could also suppress a competing speech stream by ensuring that syllables arrive during periods of low neuronal excitability.

Lateralization of frequency-specific networks for covert spatial attention to auditory stimuli.

We conducted a cued spatial attention experiment to investigate the time-frequency structure of human EEG induced by attentional orientation of an observer in external auditory space. Seven subjects participated in a task in which attention was cued to one of two spatial locations at left and right. Subjects were instructed to report the speech stimulus at the cued location and to ignore a simultaneous speech stream originating from the uncued location.

EEG classification of imagined syllable rhythm using Hilbert spectrum methods.

We conducted an experiment to determine whether the rhythm with which imagined syllables are produced may be decoded from EEG recordings. High density EEG data were recorded for seven subjects while they produced in imagination one of two syllables in one of three different rhythms. We used a modified second-order blind identification (SOBI) algorithm to remove artefact signals and reduce data dimensionality.