Roger E. Graves

Statistical power and effect sizes of clinical neuropsychology research.

Cohen, in a now classic paper on statistical power, reviewed articles in the 1960 issue of one psychology journal and determined that the majority of studies had less than a 5050 chance of detecting an effect that truly exists in the population, and thus of obtaining statistically significant results. Such low statistical power, Cohen concluded, was largely due to inadequate sample sizes. Subsequent reviews of research published in other experimental psychology journals found similar results. We provide a statistical power analysis of clinical neuropsychological research by reviewing a representative sample of 66 articles from the Journal of Clinical and Experimental Neuropsychology, the Journal of the International Neuropsychology Society, and Neuropsychology. The results show inadequate power, similar to that for experimental research, when Cohens criterion for effect size is used. However, the results are encouraging in also showing that the field of clinical neuropsychology deals with larger effect sizes than are usually observed in experimental psychology and that the reviewed clinical neuropsychology research does have adequate power to detect these larger effect sizes. This review also reveals a prevailing failure to heed Cohens recommendations that researchers should routinely report a priori power analyses, effect sizes and confidence intervals, and conduct fewer statistical tests.

Are Creativity and Schizotypy Products of a Right Hemisphere Bias

Prior research has shown associations between higher creativity (e.g., semantic association, verbal fluency), higher schizotypy (e.g., magical ideation), and relatively stronger right hemisphere laterality measures--when each of the three pairings has been studied individually. Our prior study related creativity and schizotypy to signal detection theory response criterion aspects of laterality. The present study attempted to integrate findings regarding these three constructs and to replicate the signal detection theory laterality results by providing measures of all three constructs in a within subjects design. Participants were 60 undergraduates who completed a test battery including two measures of creativity, three measures of schizotypy, a lateralized lexical decision task, and a dichotic listening task. Results are consistent with individual differences in creativity and schizotypy being partly related to a response criterion favoring right hemisphere, possibly nonconscious, processing. Dichotic listening results revealed a strong association of better right hemisphere (left ear) localization ability and creativity.

Suitability of the IBM XT, AT, and PS/2 keyboard, mouse, and game port as response devices in reaction time paradigms

The IBM PC keyboard is a convenient response panel for subjects in a reaction time task when the stimuli are presented on the same machine. However, there is a mean delay of about 10 msec and a random error of ±7.5 msec (±5 msec on the AT or PS/2). Our analyses show that for typical single response experimental situations, this added variance is acceptable. With mouse buttons, timing resulted in a delay of 31 ±2 msec if the mouse ball was steady but 45 ±15 msec if it was moving, and a 25-msec refractory period before a second response could be detected. With keys connected to the game port, timing was accurate to 1 msec. For timing the interval between two nearly simultaneous responses, only the game port method is recommended. Any research application should provide an external check on reaction timing accuracy and should correct any mean error.

Millisecond interval timer and auditory reaction time programs for the IBM PC

Many types of behavioral research require the determination of elapsed time, for example to establish interstimulus intervals and to measure reaction time. The use of an IBM PC for on-line control of such applications is limited by the poor timing resolution ordinarily available. The IBM BIOS time information that is used for the BASIC TIMER function can result in interval timing errors as great as 110 msec. A machine language subroutine is described that can provide 1-msec accuracy. A BASIC program is also described that employs this subroutine to measure auditory reaction time.

Community integration following multidisciplinary rehabilitation for traumatic brain injury.

Primary objective : To determine the extent to which participation in a multidisciplinary rehabilitation programme and patient characteristics predict improvement in community integration following mild-to-moderate traumatic brain injury (TBI). Research design : A non-randomized case-control study was conducted employing a pre-test-post-test multiple regression design. Methods and procedures : Archival data for 42 patients with mild-to-moderate TBI who completed the Community Integration Questionnaire (CIQ) at intake and again 6-18 months later were analysed. Half the sample participated in an intensive outpatient rehabilitation programme that provided multi-modal interventions, while the other half received no rehabilitation. The two groups were matched on age, education and time since injury. Results : On the CIQ Home Integration scale, participation in rehabilitation and female gender predicted better outcome. On the Productivity scale, patients with a lower age at injury had better outcome. Outcome on both of these scales, as well as on the Social Integration scale, was predicted by the baseline pre-test score (initial severity). Conclusions : Overall, multidisciplinary rehabilitation appeared to increase personal independence. It is also concluded that: (1) multivariate analysis can reveal the relative importance of multiple predictors of outcome; (2) different predictors may predict different aspects of outcome; and (3) more sensitive and specific outcome measures are needed.

More on millisecond timing and tachistoscope applications for the IBM PC

This paper describes a method of establishing time intervals at a precision of better than 1 msec, using QuickBASIC 4.0, for running real time experiments on an IBM PC without an 8087 coprocessor. This method is far superior to the TIMER function provided by BASIC, which has a precision of only 110 msec. Also described is an assembly language subroutine that corrects a problem in QuickBASIC 3.0 and QuickBASIC 4.0 to allow proper switching between screens in the CGA text mode for use of the PC as a tachistoscope. A tachistoscope program listing shows how to use the screen subroutine and how to establish intertriai intervals and record reaction times using the timing subroutines.

Is interhemispheric transfer related to handedness and gender

Interhemispheric transfer was assessed by five motor, tactile and visual tasks which required the 48 subjects to compare stimuli presented simultaneously on both sides of the body midline. Non-right-handers performed significantly better than consistent right-handers on one motor and one tactile task. Females out-performed males on the visual task and on one tactile task. Better interhemispheric transfer performance by non-right-handers and by females may be related to the reportedly larger corpus callosum regions in these groups and also to the reportedly less strong lateralization of function.

Boston Naming Test Short Forms: A Comparison of Previous Forms with New Item Response Theory Based Forms.

ABSTRACT Two new short forms of the Boston Naming Test (BNT) were developed using item response theory (IRT) with data from 206 elderly outpatients. We evaluated the diagnostic ability of 12 short forms among the full sample and in a sub-sample of 69 patients diagnosed with mild Alzheimers disease (AD) either alone or in combination with vascular dementia (VD). The full BNT (reliability alpha=.90) identified 44% of the AD/VD patients as abnormal on naming. Our 30 item short form (alpha=.90) also identified 44% of the AD/VD patients as abnormal, with 93% agreement with the full BNT on abnormal AD/VD patient classifications. Our 15 item short form (alpha=.84) identified 48% of the AD/VD patients as abnormal, with 90% agreement with the full BNTs abnormal classifications. An adaptive 30/15 item version equaled the performance of the full 30 item test while requiring only 15 items for 75% of the patients with normal naming ability. This study illustrates the utility of IRT for developing neuropsychological assessment tools.

Executive functioning as a mediator of the relationship between age and episodic memory in healthy aging

Abstract The extent to which age-related differences in executive functioning account for age-related differences in recall from episodic memory was examined in a group of healthy older adults. Fifty-one subjects between the ages of 60 and 91 years were given tests of general cognitive abilities, episodic memory, and executive functioning. A mediational model was proposed with executive functioning as the mediator of the relationship between age and delayed recall. Consistent with this model, regression analyses indicated that, when considered alone, age was a significant predictor of recall (p <.001); however, age was not a significant predictor of recall when the effect of executive functioning was partialled out of the equation (p=.37). Furthermore, the unique contribution of executive functioning accounted for 36% of the variance in recall performance. A significant portion of age-related differences in episodic memory recall, therefore, may be due to age-related differences in the executive skills re...

Conscious visual perceptual awareness vs. Non-conscious visual spatial localisation examined with normal subjects using possible analogues of blindsight and neglect

Abstract Localisation of unseen stimuli was produced with short-duration pattern-masked tachistoscopically presented targets in each of three studies with normal subjects (P<0.001). Conscious spatial attention did not influence sensitivity for this “blindsight” effect but did affect the criterion, according to a signal detection theory analysis. Unawareness of stimuli in an unattended visual field was also produced in each study (P<0.001). Conscious spatial attention decreased awareness sensitivity and increased criterion for unattended targets, leading to this “neglect” effect. As with clinical patients, greater left than right side neglect was found. This neglect asymmetry resulted from lower awareness sensitivity on the left. The blindsight and neglect effects were negatively correlated, consistent with the view that both effects reflect the function of the same visual localisation system. This system may operate without awareness, be largely unaffected by conscious attention, provide blindsight locali...