John A. Stern

Eye movements and blinks: their relationship to higher cognitive processes

Information about the timing of spontaneous eye blinks was abstracted while subjects performed a detection and identification task. We found blinks to be time-locked to saccadic eye movements involved in the identification of peripherally presented stimuli. The larger the required eye movement, the greater the likelihood of blink occurrence. Blink latencies were found to be significantly shorter for centrally, as compared to peripherally presented stimuli, and blinks were more likely to be associated with eye movement returning gaze to a central location than with movements associated with the identification of peripherally presented information. Thus, we conclude that the spontaneous or endogenous eye blink is triggered by aspects of information processing, and that blink latencies can be used as one tool for evaluating the level of complexity of such processing under a wide variety of task demands.

Effects of prolonged mental work on functional brain topography

Topographic patterns of event-related covariance between electrodes were measured from subjects performing a difficult memory and fine-motor control task for 10-14 h. Striking changes occurred in the patterns after subjects performed the task for an average of 7-9 h, but before performance deteriorated. Pattern strength was reduced in a fraction-of-a-second-long response preparation interval over midline precentral areas and over the entire left hemisphere. By contrast, pattern strength in a succeeding response inhibition interval was reduced over all areas. The pattern changed least in an intervening interval associated with visual-stimulus processing. This suggests that, in addition to the well-known global reduction in neuroelectric signal strength, functional neural networks are selectively affected by sustained mental work in specific fraction-of-a-second task intervals.

Performance and activity of hyperactive and normal boys as a function of distraction and reward

Twenty-five hyperactive boys and 25 controls matched for age, social class, and race were compared on three performance tasks (coding, tone discrimination, and connecting dots) in two settings (nondistracting and highly distracting). Control Ss performed significantly better than did hyperactives in all conditions, except during tone discrimination and connecting dots in the nondistracting setting. Distraction decreased performance for both groups on the coding task and for hyperactives on the tone discrimination task, but significantly improved performance for controls on the connecting dots task. Distraction, where detrimental, was not significantly more so for hyperactives than for controls. The effect of reward on coding performance was studied in the distracting condition; reward produced the best performance for both groups, but significant differences between groups were not found.

The Eye Blink and Workload Considerations

Two parameters of the eye blink, blink rate and blink duration, were used to assess workload in two independent operational studies. Both studies involved high fidelity strategic bomber mission simulations. The first study was an extended wartime mission where workload was evaluated during mission segments. The second study involved shorter, discrete training missions where task difficulty was systematically manipulated. Both studies produced complementary results. Results show that: (1) blink rate is significantly affected by task demands; (2) blink rate is sensitive to task modality; (3) blink duration is significantly affected by task modality and complexity; and (4) blink duration is a sensitive index of time on task effects. These data support the use of eye blink measurement in “noisy” complex environments as both a feasible and valuable assessment technique.

Elevation of Visual Threshold Associated with Eyeblink Onset

An elevation of visual threshold is found to occur shortly before the initiation of voluntary eyeblinks in human subjects, i.e., prior to the actual blocking of vision by the eyelid. This suppression of vision is discussed in terms of its possible confounding with the mechanism of saccadic suppression.

Pattern of eyelid motion predictive of decision errors during drowsiness: oculomotor indices of altered states

Sequential patterns of eye and eyelid motion were identified in seven subjects performing a modified serial probe recognition task under drowsy conditions. Using simultaneous EOG and video recordings, eyelid motion was divided into components above, within, and below the pupil and the durations in sequence were recorded. A serial probe recognition task was modified to allow for distinguishing decision errors from attention errors. Decision errors were found to be more frequent following a downward shift in the gaze angle which the eyelid closing sequence was reduced from a five element to a three element sequence. The velocity of the eyelid moving over the pupil during decision errors was slow in the closing and fast in the reopening phase, while on decision correct trials it was fast in closing and slower in reopening. Due to the high variability of eyelid motion under drowsy conditions these findings were only marginally significant. When a five element blink occurred, the velocity of the lid over pupil motion component of these endogenous eye blinks was significantly faster on decision correct than on decision error trials. Furthermore, the highly variable, long duration closings associated with the decision response produced slow eye movements in the horizontal plane (SEM) which were more frequent and significantly longer in duration on decision error versus decision correct responses.

Head Movements in Schizophrenia: New Biological Marker, Critical Neurological Flaw, or Artifact of Subvocalization?

Findings (Kolada & Pitman, 1983; Pollack & Krieger, 1958; Stevens, 1977) that schizophrenics use a combination of head and eye movements while doing tasks in which normal subjects use only eye movements were replicated using reading materials with varied line lengths. Schizophrenics (N = 12) began making head movements during silent reading at an average visual angle of 15 degrees, whereas normal subjects (N = 42) began at an average angle of 19 degrees, (p < .05). No differences were found for reading out loud. Results for a checking task (p < .01) with the same sample and for a CRT reading task (p = .05) with a smaller sample (N = 14) also indicated more use of head movements by schizophrenic subjects. Literature is reviewed suggesting that these easily observable head movements may be an especially interesting focus for schizophrenia research because of their possible relationships to pursuit tracking, dopamine metabolism, cognitive activity, and subvocalization.

Effects of text variables on eye movements in reading

Eye movement patterns in four atypical text formats were examined. Regressive eye movements were a sensitive indicator of reading disruption due to the textual manipulations of type (all capitals vs unusual) and margin (justification vs nonjustification). The capitals nonjustified format was easiest to read while the unusual justified format was most difficult. Reading speed was a less sensitive measure than regressions.

Is there eye-position-dependent facilitation of memory?

It was hypothesized that if eye-position-dependent facilitation of information retrieval underlies the phenomenon of lateral eye movements (LEMs), then subjects whose visual fixation points were assigned during both encoding and retrieval would have better recall when the points for encoding and retrieval were the same than when they were different. Sixty student volunteers gazed either straight ahead, 20 degrees right, 40 degrees right, 20 degrees left, or 40 degrees left while encoding and retrieving verbally presented word pairs. Response latency, as measured by stopwatch from audio recordings, was significantly greater for difficult word pairs when encoding and retrieval points were different, (t = 1.73, df = 59, p less than .05, one-tailed). This facilitation effect applied particularly to subjects who were nondirectional in their LEM preference. For right and left lookers, the phenomenon of shorter latency of retrieval on a verbal task when looking toward the right was found when encoding and retrieval points were different, [F(1,35) = 15 16, p less than .001], but not when they were the same [F(1,35) = .36, N.S.]. It was concluded that further studies of LEM patterns should include both encoding and retrieval and should take subject variables into account.

Cephalic and Digital Vasomotor Orienting Responses: The Effect of Response Localization, Stimulus Type and Stimulus Repetition

Two studies are reported; the first dealing with vascular responses in the head area and in finger to tone, bell and mental arithmetic stimuli, the second, with the same responses to a series of 20 tones. Dilation responses from the head area were considerably less frequently obtained to pure tone than the other three stimuli, even on first exposure. This may account for some of the disparities in results between Eastern and Western European investigators. Habituation to tone from the head, and to a lesser extent from the finger, involved a shift from vasodilative to vasoconstrictive responses. However, a series of 20 tones was not sufficient to demonstrate habituation of the vasoconstrictive response. The shift from vasodilative to vasoconstrictive responses from the head area is not concordant with Sokolovian notions of the latter response being associated with defensive responses, unless one considers the possibility that the experimental situation becomes aversive over the experimental period. This possibility is explored in the paper.