Ted Nettelbeck

Perceptual Indices of Performance: The Measurement of ‘Inspection Time’ and ‘Noise’ in the Visual System

Indices of human performance are less clear-cut than analogous measures in the physical sciences for several reasons. Variables which can alter performance include the noise upon which sensory signals are imposed, the bias shown by an observer towards one or another alternative, the use of an optional-stopping strategy for examining sensory input, and the accumulation of statistical information over time concerning the source of the input. The development of a theoretical appreciation of these variables is traced and, on this basis, a measure of the noise, which sets a limit to discriminative capacity, is suggested. The proposed index is simply the standard deviation of the best fitting normal ogive, calculated for the psychometric function obtained in a forced-choice discrimination task by the method of constant stimuli, the discriminanda being presented for 100 ms, in random order, and followed by appropriate backward masking. The index is thus closely related to traditional psychophysical measures, but is distinguished by the detailed specification of conditions under which it should be obtained. Analysis of data from previous experiments gives some indication of the order of magnitude that might be expected from a carefully controlled determination of the measure. In addition, three experiments were carried out to evaluate this suggestion, and to test its underlying rationale. In the first two, observers were required to discriminate, by pressing one of two keys, between two lines of markedly different length, exposed in random order for ten different durations. In the third, stimulus exposure was held constant, while ten different stimulus differences were presented in random order. Results from the first two experiments yielded estimates of minimum inspection time close to 100 ms, and were inconsistent with the view that observers can abandon an optional-stopping procedure of processing sensory information in favour of responding by a deadline. Measures of noise calculated in the third experiment were of the order expected on the proposed rationale, while response latencies were again inconsistent with the notion of deadline responding. Further analysis of the results of the three experiments suggests that measures of inspection time and noise, together with a third index related to the degree of caution exercised by an observer, appear to be stable and consistent descriptors of performance. The wider implications of the successful use of this kind of perceptual index of performance are discussed with reference to the measurement of visual acuity, as a means for detecting effects of environmental stress, and as a conceptual framework for the understanding of individual differences.

Inspection time: an index for intelligence?

Recent publicity has been given to reports of high correlations between IQ and “inspection time”, a measure derived from simple discrimination which is assumed to provide an estimate of the time taken by a basic component of the decision process. However, this publicity has not recognised that the inclusion of mentally retarded participants in the experiments concerned may have led to inflated correlations, because of the marked extent to which the performance of retarded subjects is inferior to that of nonretarded subjects. Evidence from the performance of nonretarded subjects in three studies suggests that although speed of decision is related to IQ, the degree of association is smaller than recent publicity has suggested. Inspection time does not appear at present to hold promise as an index from which a “culture-fair” measure of intelligence might be derived.

Aging, Cognitive Performance, and Mental Speed.

Abstract Measures of four-choice reaction time (RT), inspection time (IT), and scores on a speed coding-substitution task obtained from 104 subjects aged from 54 to 85 years were found, separately or together, to account for almost all age-related changes in cognitive performance on a number of performance indices reflecting general fluid ability. However, measures of information-processing speed did not entirely predict some aspects of memory performance. These correlations were not due to the inclusion of persons who had lower than average IQ scores or who were over 80 years old, or to the fact that some psychometric tests were scored to a time limit. The results also showed that higher intelligence does not serve to protect against the effects of aging, because rates of decline with age in scores on tests of spatial ability, and in memory and in information-processing tasks were the same within two subgroups selected for higher and lower verbal crystallized abilities.

Measures of timed performance and intelligence

The question of an association between IQ and measures of timed performance derived from inspection time and reaction time was examined in a sample of 182 adults and by reanalyzing data involving 48 adults from a previously published study. Multiple regression analysis found that measures of timed performance accounted for as much as 25% of IQ variance in the normal population, but that the inclusion of borderline and mildly retarded subjects resulted in much higher correlation coefficients because of the markedly less efficient performance of these persons in tasks of this kind. This outcome raised doubts about the validity of combining data from retarded and nonretarded subjects. Results ran counter to claims that tasks of the kind used are largely uninfluenced by cognitive variables, so that findings are not necessarily explained satisfactorily in terms of a mental speed factor. It was concluded that these measures of timed performance do not, at this time, provide a basis from which a reliable culture-fair measure of intelligence might be devised.

A meta-analysis of the effects of chemotherapy on cognition in patients with cancer.

OBJECTIVE The aim of this meta-analysis was to assess whether chemotherapy-related cognitive impairment is consistently observed in cancer patients and to identify the areas of cognition affected. METHODS The meta-analysis included 13 studies and examined the effects of chemotherapy on seven different cognitive domains, across five cancer types. It was the intention of this meta-analysis to stringently exclude many studies, allowing for examination of cognition in carefully selected studies of chemotherapy recipients who do not have current mood or anxiety diagnoses (or psychiatric or substance abuse histories), without brain cancer and who have not had radiotherapy or hormone treatment. A moderator analysis examined whether patient age, treatment duration and time since treatment end significantly contributed to chemotherapy-related cognitive impairment. RESULTS Evidence for the presence of cognitive impairment following cancer treatment was established for executive function and memory. No relationship was found between cognitive impairment and time since treatment cessation but a significant negative relationship was found for treatment duration. Age had no impact on treatment-related cognitive impairment. CONCLUSIONS Future research must be conducted on chemotherapy-related cognitive impairment in cancer types such as lymphoma and leukaemia, which have received a moderate amount of attention and colorectal cancer, which has received little attention. This would enable us to determine the extent to which chemotherapy-related cognitive impairment is a universal phenomenon associated with the cancer experience and its treatment regardless of cancer type.

Inspection Time in the Structure of Cognitive Abilities: Where Does IT Fit?.

Abstract Inspection time (IT) correlates with IQ. This study had four aims: to locate IT within a hierarchical model of cognitive abilities; to test if IT has properties not tapped by other backward masking tasks; to test whether decision time (DT) from ‘odd-man-out’ (OMO) reaction time (RT) measures the same basic process as IT; and to test whether Wechsler performance IQ (PIQ) measures fluid ability (Gf). A battery of psychometric and chronometric tests was administered to 90 adults. Exploratory factor analysis showed that IT loaded on a general speediness factor and a higher-order general ability factor (G) but not on Gf. The results were similar for an alphanumeric pattern backward masking task suggesting that IT does not have special status as a backward masking task. DT and IT measured different processes and PIQ did not measure Gf. Confirmatory factor analyses compared results across alternative models of cognitive abilities but without differentiating one above the others. We conclude that IT does not measure fluid ability, but the question of whether information-processing speed is common to all cognitive abilities is still open.

The Flynn Effect: Smarter Not Faster

Inspection time (IT) and Peabody Picture Vocabulary Test (PPVT) scores from 75 school children aged 6–13 years in 2001 were compared with the performances of 70 children aged 6–13 years who had attended the same primary school in 1981 [J. Exp. Child Psychol. 40 (1985) 1.]. ITs for the 2001 sample were measured with the same four-field tachistoscope and identical computer-based procedures followed by Wilson in 1981. The 2001 sample completed two versions of PPVT concurrently: PPVT (1965, Form A) as used in 1981 and PPVT-III (1997, Form IIIA). Mean ITs from both samples, 20 years apart, were essentially the same (123±87 and 116±71 ms in 1981 and 2001, respectively). There was, therefore, no evidence that speed of processing had improved. Correlations between IT and raw PPVT scores were significant (P<.01) for both 1981 (r=−.43) and 2001 (r=−.31). Within the 2001 sample, concurrent PPVT scores correlated .68; however, means revealed a significant Flynn effect. Thus, scores for the 2001 cohort on the earlier PPVT were higher (M standardized IQ 118.52±16.62) than the recently restandardized PPVT-III (113.97±12.23), although, compared in terms of the most recent standardization sample, the 2001 cohort was equivalent to the 1981 sample (113.66±16.72). The Flynn effect has nothing to do with speed of processing as measured by IT, despite the effect being strongest for ability tests that earn bonus scores for quick performance. Because IT correlates with IQ but appears to be stable across 20 years, whereas IQ is not, IT may have promise as a useful biological marker for an important component of cognitive decline during old age.

A comparison of dry-bed training and standard urine-alarm conditioning treatment of childhood bedwetting

Two experiments examined the significance of patient-therapist contact in the treatment of childhood nocturnal enuresis by behavioural methods. The first involving 45 enuretic children compared the effectiveness of the standard urine-alarm conditioning procedure when it is closely supervised as opposed to not supervised after the initial description of training. Results showed that adequate patient-therapist contact is necessary for the effective use of the standard conditioning treatment. One hundred and twenty children took part in the second experiment which compared standard conditioning with Dry-Bed Training (DBT) (Azrin et al, 1974) administered under four different conditions—by the childs parents at home, by a professional trainer at home, by a professional trainer in hospital and by the childs parents without the adjunct of a conventional bed-buzzer device. DBT was superior to standard conditioning in terms of the proportion of bedwetters successfully treated and in terms of the speed of treatment. DBT was equally effective under all conditions of administration except where it did not have the adjunct of a machine, in which case it was only marginally better than no treatment at all.

Correlation between Inspection Time and Psychometric Abilities: A Personal Interpretation.

Abstract More than 25 years of research suggests that the measure inspection time (IT) does capture low-level aspects of cognitive functioning that contribute to human intelligence. However, recent evidence does not support earlier claims that IT estimates the speed of a single mechanism like “sampling input” or “apprehension.” Rather, together with other tasks that employ pattern backward masking to limit the duration for which information is available for processing, IT is probably sensitive both to focused attentional capacities to detect organization and change under severe time constraints and to decision processes, ongoing beyond mask onset, that monitor responding. Among normal young adults, IT is correlated with the broad psychometric factor Gs (“speediness”). This mediates correlation with general intelligence. In this group, IT is not correlated with Gf. However, whether this outcome generalizes to samples of persons with an intellectual disability, to young children, or to elderly persons is not yet known. Psychological processes underpinning IT are currently only speculatively defined, but it should prove possible to unravel these by experimentation. To this end, backward masking procedures are arguably more theoretically tractable than reaction time tasks because they reduce the impact of higher-level cognitive strategies on performance. On this basis, IT may hold promise as a means for developing partial explanations for intelligence in psychological terms. However, whether this is realized depends on identifying the psychological functions that support IT.

Dose-related effects of alcohol on cognitive functioning

We assessed the suitability of six applied tests of cognitive functioning to provide a single marker for dose-related alcohol intoxication. Numerous studies have demonstrated that alcohol has a deleterious effect on specific areas of cognitive processing but few have compared the effects of alcohol across a wide range of different cognitive processes. Adult participants (N = 56, 32 males, 24 females aged 18–45 years) were randomized to control or alcohol treatments within a mixed design experiment involving multiple-dosages at approximately one hour intervals (attained mean blood alcohol concentrations (BACs) of 0.00, 0.048, 0.082 and 0.10%), employing a battery of six psychometric tests; the Useful Field of View test (UFOV; processing speed together with directed attention); the Self-Ordered Pointing Task (SOPT; working memory); Inspection Time (IT; speed of processing independent from motor responding); the Traveling Salesperson Problem (TSP; strategic optimization); the Sustained Attention to Response Task (SART; vigilance, response inhibition and psychomotor function); and the Trail-Making Test (TMT; cognitive flexibility and psychomotor function). Results demonstrated that impairment is not uniform across different domains of cognitive processing and that both the size of the alcohol effect and the magnitude of effect change across different dose levels are quantitatively different for different cognitive processes. Only IT met the criteria for a marker for wide-spread application: reliable dose-related decline in a basic process as a function of rising BAC level and easy to use non-invasive task properties.