Relationships between overt behavioral measures such as Reaction Time (RT) and response accuracy (percent correct, A') and psychophysiological indices of oculomotor, electroencephalographic and cardiovascular activity were delineated within the context
of a 50 min continuous performance task. Effects associated with either Time On Task (TOT) and/or variations in instantaneous information processing load were obtained in all measurement domains.
Subjects maintained comparable mean performance levels (for both RT and accuracy measures) across early, middle and late segments of the task. Similarly, the mean values of Event Related brain Potential (ERP) indices of cognitive processes (i.e. the
P300 and CNV components) remained constant across task segments. However, variability in response speed and accuracy did increase with TOT. This increased response variability with TOT was associated with increased blink durations, decreased post-stimu
lus blink latencies, decreased anticipatory and reactive saccade velocities and amplitudes as well as fewer and later reactive saccades. Later task segments also contained increased numbers of EEG transients associated with decreased alertness, decreased
stimulus-locked theta, low alpha and gamma band EEG hypersynchronizations, increased heart rate variability and respiratory sinus arrythmia variability scores, as well as decreased power in the 0.10 Hz band of the cardiac variability power spectrum.
Effects due to variations in instantaneous information processing load were most evident in the periods surrounding a target (imperative) stimulus. In anticipation of a target stimulus, subjects demonstrated an increased cardiac decelerative response
, desynchronization in the middle and high alpha bands, and increased CNV amplitudes. The period following an imperative stimulus was characterized by an increase in the amplitude of the P300 component, decreased late theta power, increased late gamma po
wer, and increased middle and high alpha band hypersynchronizations. While blinks were inhibited prior to all stimuli, the post-stimulus period of inhibition was longest following imperative stimuli. Target stimuli were also associated with more efficie
nt anticipatory eye-movements.
Importantly, several within-subject relationships between trial-to-trial performance variability and oculomotor metrics were found. In the absence of a blink, RTs were substantially delayed. When blinks were present, very short latency blinks were as
sociated with more variable RTs and increased errors. If blink latencies were late, RTs were late as well. Trials containing especially long duration blinks were associated with decreases in performance accuracy. Target stimuli followed by reactive sac
cades were responded to more slowly and with less accuracy than when effective anticipatory eye-movements preceded stimulus onset. Furthermore, the larger the amplitude of the reactive saccade, the greater the increase in RT. Abstracting peripheral info
rmation (recheck saccades) also incurred a cost in terms of increased RT -- and the slower the velocity of the recheck saccade the greater the impact upon RT. Finally, exploratory multi-variate modelling of the overt performance data indicated the degree
to which both within as well as between-subject variability could be accounted for by various combinations of the psychophysiological measures.
