Is there a sex difference in human laterality? IV. An exhaustive survey of dual-task interference studies from six neuropsychology journals.

The entire contents of six neuropsychology journals (161 volumes, 612 issues) were screened to identify dual-task laterality experiments. Of 112 experiments thus identified, 45.5% provided information about sex differences. Although 23 experiments yielded at least one significant main effect or interaction involving the sex factor, only 5 outcomes represented an unambiguous sex difference in laterality. All 5 of those sex differences support the hypothesis of greater hemispheric specialization in males. The confirmatory outcomes constitute less than 10% of the informative experiments and less than 5% of the total population of experiments. These data alone do not rule out the possibility that sex differences are chance findings (Type I errors). However, when considered along with similar results from perceptual laterality data previously examined, the dual-task data fit the pattern of a small but reliable population-level sex difference in human laterality.

Allocation of attention in dichotic listening: effects on the detection and localization of targets within lists.

In each of two dichotic listening experiments, 48 normal right-handed adults were instructed to attend selectively to the left and right ears and to divide attention equally between ears. Participants listened for specified targets and reported the ear of entry when the target was heard. Stimuli consisted of lists of digit names in Experiment I and lists of words in Experiment 2. Shifts of attention altered ear asymmetry for localizing but not for detecting digit names. For words, attention shifts altered both detection asymmetry and localization asymmetry, but the effect of attention on detection seemed to reflect differential retrieval from short-term memory rather than differential perception. In both experiments, shifting attention toward either ear resulted in a reporting bias such that signals were attributed to the attended ear more often than to the unattended ear. The results confirm our previous findings, for single pairs of stimuli, that volitional shifts of attention alter response selection rather than perception.

Allocation of attention in dichotic listening: differential effects on the detection and localization of signals.

In 2 dichotic listening experiments, 96 normal right-handed adults attended selectively to the left and right ear and divided their attention equally between both ears. Participants listened for specified targets and reported the ear of entry. The material consisted of pairs of consonant-vowel syllables in Experiment 1 and pairs of rhyming consonant-vowel-consonant words in Experiment 2. Both experiments yielded a right-ear advantage for detection and for localization. Attention instructions had no effect on detection. However, focusing attention on 1 ear increased the number of targets attributed to that ear while decreasing the number of targets attributed to the opposite ear. The dissociation between detection and localization indicates that volitional shifts of attention influence late (response selection) processes rather than early (stimulus identification) processes. Selective-listening effects can be accounted for by a 2-stage model in which a fixed input asymmetry is modulated by a biased selection of responses.

Is there a sex difference in human laterality? III. An exhaustive survey of tactile laterality studies from six neuropsychology journals.

The contents of six neuropsychology journals (161 volumes, 612 issues) were screened to identify tactile laterality experiments. Of 73 experiments identified, 40% provided information about sex differences. Seventeen experiments yielded a total of 18 sex differences, of which 4 could be interpreted in terms of the hypothesis that functional cerebral lateralization is more pronounced in males. All 4 interpretable outcomes (constituting 5.5% of the population of experiments and 13.8% of the informative experiments) were found to be consistent with the differential lateralization hypothesis. The results, in isolation, do not justify rejecting the null hypothesis. However, when considered in conjunction with findings for auditory and visual laterality studies, the present results are compatible with a weak population-level sex difference.

Use of the Brief Psychiatric Rating Scale to measure success in a psychosocial day program.

This study contrasted six subscales of the Brief Psychiatric Rating Scale (BPRS) to determine their sensitivity to psychosocial treatment outcome. An expanded version of the BPRS was administered to 216 clients on admission to a day program. The subscale measuring hostility and suspiciousness discriminated at intake clients who were therapeutically discharged from clients who did not complete the program and predicted discharge status after the investigators controlled for the effects of demographic variables. Significant reductions in scores were obtained on five subscales for a subset of clients to whom the BPRS was readministered before discharge. The results support the use of the expanded BPRS as an evaluative tool in psychosocial rehabilitation programs.

Asymmetry of verbal-manual interference: dissociation between rate and variability in left-handers.

In two experiments, 48 right-handed and 48 left-handed adults, respectively, performed speeded and consistent finger tapping with and without concurrent oral reading. Interference was measured in terms of change in tap-to-tap rate and variability. Experiment 1 confirmed a previous report that concurrent reading decreases the rate of speeded finger tapping and increases the rate of consistent tapping in right-handers, and that the right hand is affected more than the left. Experiment 2 showed that, for left-handers, concurrent reading decreases the rate of left-hand tapping more than right-hand tapping but increases the variability of the right hand more than the left. The double dissociation in left-handers between hand and dependent variable suggests that the speed and variability reflect different mechanisms of intertask interference. More generally, the findings illustrate the multidimensionality of motor performance and the risk of making inferences about neural organization on the basis of a single dependent measure.

Is there a sex difference in human laterality? II. An exhaustive survey of visual laterality studies from six neuropsychology journals.

The contents of six neuropsychology journals (98 volumes, 368 issues) were screened to identify visual half-field (VHF) experiments. Of the 516 experiments identified, 42% provided information about sex differences. Sixty-eight experiments yielded a total of 92 sex differences, 23 of which met stringent criteria for sex differences in laterality. Of the 20 sex differences satisfying stringent criteria and lending themselves to interpretation in terms of the differential lateralization hypothesis, 17 supported the hypothesis of greater hemispheric specialization in males than in females. The 17 confirmatory outcomes represent 7.8% of the informative experiments. When less stringent criteria were invoked, 27 outcomes (12.3% of the informative experiments) were found to be consistent with the differential lateralization hypothesis. Six findings were contrary to the hypothesis. The results, which closely resemble results for auditory laterality studies, are compatible with a population-level sex difference that accounts for 1 to 2% of the variance in laterality.

Is there a sex difference in human laterality? I. An exhaustive survey of auditory laterality studies from six neuropsychology journals.

The entire contents of six neuropsychology journals (98 volumes, 368 issues) were screened to identify auditory laterality experiments. Of the 352 dichotic and monaural listening experiments identified, 40% provided information about sex differences. Among the 49 experiments that yielded at least one significant effect or interaction involving the sex factor, 11 outcomes met stringent criteria for sex differences in laterality. Of those 11 positive outcomes, 9 supported the hypothesis of greater hemispheric specialization in males than in females. The 9 confirmatory outcomes represent 6.4% of the informative experiments. When less stringent criteria were invoked, 21 outcomes (14.9% of the informative experiments) were found to be consistent with the differential lateralization hypothesis. The overall pattern of results is compatible with a weak population-level sex difference in hemispheric specialization.

Diagnostic utility of the MCMI-I and MCMI-II with psychiatric outpatients.

Research indicates that the Millon Clinical Multiaxial Inventory (MCMI-I) lacks diagnostic accuracy when compared to clinically generated DSM-III-R diagnoses. This shortcoming is most evident for the identification of psychotic disorders. The MCMI-II was designed to reflect more accurately the DSM-III-R diagnostic formulation, but its diagnostic efficacy has yet to be determined with clinical samples. In the present investigation, two consecutive samples of psychiatric patients who were attending an outpatient day treatment program were administered either the MCMI-I (N = 39) or the MCMI-II (N = 37). MCMI diagnoses were compared with clinician-generated DSM-III-R diagnoses. Relative to clinical judgment, both versions of the MCMI underestimated the incidence of psychotic disorders and overestimated the incidence of nonpsychotic disorders and personality disorders.

Amino acid transport in multidrug-resistant Chinese hamster ovary cells.

In the process of assessing the effect of anthracycline drugs on cellular membrane function in cultured multidrug resistant (MDR) and its parental cells, experiments were undertaken to investigate the kinetics of neutral amino acid membrane transport (the sodium dependent A and ASC systems). P-glycoprotein, a high molecular weight energy requiring integral membrane protein responsible for actively pumping drugs out of cells, has been shown to be overexpressed in MDR cells. It was our hypothesis that its presence might affect other membrane energy requiring systems such as amino acid transport. On establishing the concentrations of P-glycoprotein by western blotting in the two cell lines to be studied, the kinetics of membrane transport of the neutral amino acids alpha-aminoisobutyric acid (AIB) and serine (SER) were investigated using the CHRC5 multidrug resistant and AUX B1 parental Chinese hamster ovary (CHO) cells. In CHRC5 cells, the amount and rate (Vmax) of accumulated amino acids, was significantly depressed when compared to AUX B1 cells, however, there was no difference in the rates of amino acid efflux between these two cell lines. Using 1,6-diphenyl 1,3,5-hexatriene (DPH) polarization to evaluate the state of membrane fluidity in the two cell lines studied, it was seen that CHRC5 cells showed a slightly lower degree of polarization than that observed in AUX B1 cells. These results suggest, that the P-glycoprotein does not alter amino acid transport directly but may modify the activity or numbers of functional transport carriers.

Sex differences and the role of figural complexity in determining the rate of mental rotation.

Two experiments were conducted to investigate the effects of figural complexity on the rate of mental rotation of 3-dimensional figures and to compare the performance of men and women. Complexity was manipulated in three ways: by changing the number of blocks in the figure (7 or 10), by altering the number of turns (2 or 3), and by using outline or solid figures. In the first study, these factors were manipulated between groups of subjects. Women showed steeper slopes than men, but none of the complexity variables affected either slope or intercept for the mental rotation function. In the second study, number of turns and number of blocks were manipulated within-subjects, using only the solid figures. There were significant sex differences in both slope and intercept, and the number of blocks affected the slope of the rotation function. In both studies, a small percentage of the subjects showed nonlinear functions relating angular rotation to response time. Although the women consistently showed slower rotation functions, rate of rotation did not relate either to figural complexity or to nonlinearity. The results suggest that the rate of mental rotation is not affected by figural complexity, at least at the levels used in the present study, and that men and women employ essentially similar strategies.

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.