Merrill Hiscock

Refining the forced-choice method for the detection of malingering.

For seven years following head trauma, a 45-year-old restaurant owner had claimed that he was unable to work because of impaired memory. A specially designed forced-choice memory test yielded performance significantly below the chance level and thus indicated malingering. This case illustrates some means of increasing the utility of forced-choice malingering tests.

Asymmetry of verbal-manual time sharing in children: A follow-up study

Abstract Normal, right-handed children between the ages of 3 and 12 yr engaged in unimanual finger tapping with and without concurrent speech. Cross-sectional data from 155 children showed that vocalization disrupted right-hand tapping more than left-hand tapping, and that the degree of asymmetry did not vary with age. These results support the developmental invariance hypothesis of language lateralization. Longitudinal data for 115 children likewise failed to show any increase in performance asymmetry over a 1-yr interval. Group data are stable over time, but the unreliability of individual asymmetry scores militates against the use of time-sharing asymmetry as an index of individual differences in speech lateralization.

Verbal-manual time sharing in children as a function of task priority

Eighty-three normal, right-handed children performed unimanual finger tapping recitation of a tongue twister, and both tasks concurrently. Trade-offs in dual-task performance were measured as the priority assigned to each task was manipulated. Irrespective of task priority, speaking interfered to a greater degree with right-hand tapping than with left-hand tapping, but the effect of tapping upon verbal production and speech errors was not lateralized. The asymmetric effect of speech upon tapping, which was seen in 85.5% of the children, cannot be attributed to the disparity between hands in baseline tapping rate. The findings suggest that time-sharing asymmetry reflects cerebral lateralization of speech, but only some of the results would be predicted on the basis of a functional distance principle of cerebral organization.

Concurrent performance of rhythmically compatible or incompatible vocal and manual tasks: Evidence for two sources of interference in verbal-manual timesharing

Forty-two normal, right-handed adults performed rhythmic finger tapping with the left or right hand while concurrently reciting sentences that were either compatible or incompatible with the rhythm being tapped. Both kinds of sentences slowed tapping equally, and the interference was lateralized so that the right hand was affected more than the left. In contrast, the regularity of finger tapping was disrupted to a much greater degree by incompatible sentences than by compatible sentences, and the effect was comparable in the left and right hands. The results implicate two mechanisms of verbal-manual interference--capacity limitation and timing constraints--and thus reconcile certain inconsistencies among findings from previous concurrent-task studies.

The lengthy persistence of priming effects in dichotic listening.

A dichotic digits task, with selective listening instructions, was administered to 72 normal, right-handed children. The interval between monitoring one ear and monitoring the other ear was either 5 min or 1 week. Ear asymmetry depended on the order in which the ears were monitored: only children who listened first to the right ear showed a right-ear advantage. This order, or priming, effect was equally strong irrespective of the interval over which attention was switched. The results show that attentional biases may exert a strong and enduring influence on ear asymmetry.

Rate and variability of finger tapping as measures of lateralized concurrent task effects

Using a sample of 48 normal right-handed adults, we assessed the effects of oral reading on concurrent unimanual finger tapping under all combinations of instructional set (speeded vs. consistent tapping), tapping movement (repetitive vs. alternating), task emphasis (reading emphasized vs. tapping emphasized), and tapping hand. Change in tapping rate and variability was measured relative to the corresponding single task control condition. Reading decreased the rate of speeded finger tapping but increased the rate of consistent tapping. In both instances, the right hand was affected more than the left hand. Asymmetries were comparable for repetitive and alternating tapping. When measured in terms of variability, however, effects were largely symmetric. The findings clarify the conditions under which lateralized concurrent task effects are most likely to occur and show that such effects are not statistical artifacts. It appears that subjects attempt to coordinate the timing of concurrent activities and that speech timing is more strongly linked to right-hand control than to left-hand control in right-handers.

Dual Task Performance in Children: Generalized and Lateralized Effects of Memory Encoding upon the Rate and Variability of Concurrent Finger Tapping

Interference between concurrent tasks was used to investigate the brain basis of capacity limitations apparent when children encode information. Seventy-three right-handed children in Grades 1-4 engaged in speeded unilateral finger tapping while encoding a variable number of faces or numbers for subsequent recognition testing. With both face and number encoding, tapping rate decreased as memory load increased. Encoding numbers was more disruptive than encoding faces. Both encoding tasks slowed right-hand tapping more than left-hand tapping, relative to control tapping performance, but had only a bilateral effect on the variability of tapping. Although overall interference was less than that observed with a comparison task (i.e., speaking), the asymmetry of interference was comparable. The results suggest that cerebral lateralization for memory encoding, as well as for speech, is constant across the age range of 6-10 years. Findings regarding developmental change in overall capacity, however, are task specific: interference from speaking but not from memory encoding decreases with increasing age.

Effects of speaking upon the rate and variability of concurrent finger tapping in children

Abstract Tapping rate and variability were measured as 73 normal, right-handed children in Grades 1–4 engaged in speeded unimanual finger tapping with and without concurrent recitation. Speaking reduced the rate of tapping and increased its variability to a greater extent in younger children than in older children. Developmental changes in variability but not rate were attributable to a greater number of lengthy (>500 ms) pauses in the tapping of younger children. Speaking slowed the right hand more than the left, and the degree of this asymmetry was constant across grade levels. The right-hand effect for tapping rate was not attributable to lengthy pauses. In contrast, asymmetric increases in tapping variability occurred only among children in Grade 1 and only when lengthy pauses were included in the data. The results implicate three mechanisms of intertask interference: one involving capacity limitations, a second involving cross-talk between motor control mechanisms for speech and finger movement, respectively, and a third factor involving occasional diversion of attention from tapping to speaking. These mechanisms are discussed in relation to developmental changes in mental capacity.

Laterality and Dyslexia: A Critical View.

The study of learning disabilities has entered an era in which neural models play a primary role (Chall and Mirsky, 1978; Cruickshank, 1980; Gaddes, 1980; Kinsbourne and Caplan, 1979; Knights and Bakker, 1976). Factors such as family dynamics, emotional adjustment, and motivation, which attracted considerable attention from learning-disability specialists in the past, have been de-emphasized in favor of neurological factors such as perceptual and attentional disorders, neurodevelopmental lag, and cerebral dominance. In this respect, Samuel Ortons (1937) general position with respect to the neural basis of learning disability--a minority viewpoint in the 1920s and 1930s---has become established in the mainstream of contemporary thinking about dyslexia and associated disorders. Prominent among the neural models of dyslexia are those that attribute reading disorders to a defect in cerebral dominance. Thus, not

Ocular motility as an indicator of verbal and visuospatial processing

Three experiments were conducted to study ocular motility as a function of cognitive task. Horizontal eye movements were recorded electrically as normal adults attempted to answer auditorily presented questions that were either verbal-conceptual or visuospatial in nature. In each of the three experiments, verbal-conceptual questions elicited significantly more eye movements than did visuospatial questions. Direction of initial movement was a less reliable indicator of question category. Experiment 1 showed that the difference in eye movement rate associated with question category persisted throughout the period of deliberation; in Experiment 2, consistent differences in ocular motility were obtained with diverseverbal-conceptual and visuospatial questions; Experiment 3 showed that the effect is found even when an oral answer is not required. These findings cannot be attributed to differences in task difficulty or response factors. A low eye movement rate may facilitate visual thinking by reducing interference from the environment, or it may reflect bilateral activation of the cerebral hemispheres.