Karl Van Orden

Selective attenuation in brightness for brief stimuli and at low intensities supports age-related transient channel losses.

A brightness estimation experiment was conducted on 10 old (ages 60 to 77) and 10 young (ages 22 to 27) volunteers. Participants were introduced to magnitude estimation by scaling the lengths of line stimuli, after which they dark adapted for 10 minutes. Stimuli for brightness estimation were presented binocularly via a free-viewing system and consisted of circular flashes of 2 degrees. Stimuli covered a 3 log unit range of luminance levels in 0.5 log unit steps, and 3 durations (10, 100, 1000 msec). Linear regression analysis yielded dual-branched functions with a low intensity segment which was significantly steeper in slope than the high intensity segment. The slope for the older group was significantly less steep than that of the younger observers only at the low intensity segment. Findings with respect to stimulus duration showed a significantly attenuated slope for the old as compared to the young group only at 10 msec. The results extend previous threshold results to suprathreshold levels, and are consistent with an hypothesis of a selective loss of transient channels with age.

NEUROPSYCHOLOGICAL IMPLICATIONS OF HAND PREFERENCE VERSUS HAND GRIP PERFORMANCE

Hand-grip strength, measured by a hand dynamometer, was compared with hand preference for writing in a sample of 173 male and female undergraduate students. Hand preference and performance correlated significantly, but superiority of hand grip for 24% of the subjects did not coincide with the preferred hand. Hand-grip performance was not an accurate predictor of hand preference, and neuropsychological inferences on the basis of hand performance should be made cautiously. No significant differences were found between the right/left ratio scores for males and females, or order conditions.

Augmenting task-centered design with operator state assessment technologies

Task-Centered Design (TCD) of human-system interfaces focuses on supporting the user throughout all phases of tasks, from initiation to completion. TCD typically requires software that monitors aspects of system information to trigger tasks, develop user-friendly information sets, propose task solutions and actions, and confirm actions as directed and approved by the operator. The operator monitors tasks awaiting completion on a Task Manager display. We demonstrate that moment-to-moment operator workload monitoring is greatly facilitated by TCD. Workload estimates were obtained every 2-min over the course of a 35-min test session during an air defense command and control scenario. Workload was readily modeled by the task loading, and the density of track icons on the display. A second study related the unitary workload estimates to NASA TLX workload subscales. Unpublished data from our laboratory indicated that eye activity measures (e.g., blink frequency and duration, pupil diameter, fixation frequency and dwell time) did not improve the estimation of workload. These findings indicate that at least for well-executed TCD systems, eye tracking technologies may be best employed to monitor for fatigue and incongruities between the focus of attention and task requirements. Recent findings using EEG hold promise for the identification of specific brain signatures of confusion, orientation, and loss of situational awareness. Thus the critical element of human directed systems is good initial design. Understanding of the task will lead to system automation that can balance the workload of the operator, who is functioning in a normal state. However, physiological monitoring will be most useful if operators veer beyond their normal conditions and are confused, overloaded, disoriented or have other impairments to their abilities. By detecting the operators loss of function early, inappropriate operator inputs can potentially be avoided.

61.2: Eye Movements During Visual and Auditory Task Performance

Abstract : The primary focus of this research effort was the tracking of eye movements during complex cognitive tasks. 8 volunteers performed a visual tracking task alone and a combination of the visual task and the auditory Paced Serial Addition Task (PASAT). Results showed a reduction in range on the order of 50% for eye movements and an increase in variability of vergence eye movements during the dual task. This change can be characterized as visual tunneling.

Context effects in brightness estimation.

Under what conditions do briefly presented flashes yield steeper brightness functions than do flashes of longer duration? The brightness of flashes subtending 2° or 4° and varying in luminance from 216 to 216 cd/m2 were judged by magnitude estimation. Only when durations of 10, 100, and 1,000 msec were randomly intermixed did the short-duration (10-msec) function have a steeper slope; presenting 10-msec durations alone or intermixing 30- and 1,000-msec durations produced no steepening of the short-duration (10- or 30-msec) functions. The steeper brightness functions found for brief flashes in this and previous experiments may be contextually based, that is, dependent upon the presence of longer duration stimuli.

Eye Movement Measures of Performance on Visual Search Tasks: Equating the Baselines of Task Performance

Previous research suggests that eye measures can indicate decrements in performance on a visual tracking task due to increased difficulty in task execution from fatigue-induced conditions (Van Orden, 2000). In order to examine the sensitivity of eye movement to increased cognitive workload as indicated by difficulty of task, we chose a visual search paradigm. Using a basic visual search task, we studied the effects of increased task difficulty on subject performance and their corresponding eye measures. Results show a decrease in performance as the number of objects on the screen increase. What results could be expected if differences in individual abilities to perform visual search were controlled? This experiment looks at one method that can be used to control for individual differences in visual search abilities.

Spatial Frequency-Dependent Asymmetry of Visual Evoked Potential Amplitudes

The extent to which pattern reversal evoked potential amplitudes are distributed symmetrically over the scalp was investigated as a function of stimulus spatial frequency. Nine right-handed male subjects viewed sinusoidal grating stimuli of 4.0 and 0.5 c/deg phase reversed every 900 msec. A visual half-field configuration enabled selective stimulation of the right- or left-hemisphere visual cortex. Evoked responses were recorded from the 2 cm above the inion (Oz) and at 7 and 13 cm lateral to Oz. Analyses of normalized evoked response amplitudes showed a significant asymmetry for the 4.0 c/deg stimulus; right-hemisphere amplitudes declined as a function of distance from the midline, while left-hemisphere amplitudes were greatest at the 7 cm recording site. No hemispheric differences were observed for the 0.5 c/deg stimulus; amplitudes for both hemispheres declined as a function of distance from the midline. The data are discussed in terms of hemispheric differences in morphology and functional asymmetries at early levels of sensory processing.