N A Taroyan | PubMed Health

PubMed2002

Effect of signal length on the performance of independent component analysis when extracting the lambda wave.

The aim of the study was to investigate the effect of signal length on the performance of a signal source separation method, independent component analysis (ICA), when extracting the visual evoked potential (EP) lambda wave from saccade-related electro-encephalogram (EEG) waveforms. A method was devised that enabled the effective length of the recorded EEG traces to be increased prior to processing by ICA. This involved abutting EEG traces from an appropriate number of successive trials (a trial was a set of waveforms recorded from 64 electrode locations in a study investigating saccade performance). ICA was applied to the saccade-related EEG and electro-oculogram (EOG) waveforms recorded from the electrode locations. One spatial and five temporal features of the lambda wave were monitored to assess the performance of ICA applied to both abutted and non-abutted waveforms. ICA applied to abutted trials managed to extract all six features across all seven subjects included in the study. This was not the case when ICA was applied to the non-abutted trials. It was quantitatively demonstrated that the process of abutting EEG waveforms was useful for ICA preprocessing when extracting lambda waves.

Adult↗

PubMed2000

Exploring sequential stereopsis for co-planarity tasks.

We used the sequential stereopsis paradigm and apparatus described by Enright (Vision Research, 36, (1996) 307-312). The observer's task was to set targets to equidistance in Experiments 1-3, and to make them co-planar in Experiment 4. However, it is argued that in all experiments observers exploited a co-planarity setting strategy. Sequential stereopsis produced good performance throughout in terms of low disparity thresholds when head position was varied by rotations around three axes: vertical (azimuth condition); horizontal (elevation); and midline (tilt). It also produced good performance when the targets were shifted in position so that they both lay on one side of the median plane of the head. These results cannot be accounted for by Enright's isovergence hypothesis unless it is extended to incorporate other information about eye positions. Performance was better but not greatly so in control simultaneous stereopsis conditions, nor did it deteriorate much when the observer's view was restricted solely to the targets by removing visibility of the room in which the apparatus was located. Target settings were typically located on a concave arc centred on the median plane. This effect was quantitatively modelled using disparity correction for a relief task of co-planarity (Gârding, Porrill, Mayhew, & Frisby. Vision Research, 35 (1995) 703-722). This modelling indicated over-estimations of c.10-20 cm in fixation distance for target distances in the range 71.5-112.5 cm.

Adolescent↗