An exact statistical method for comparing topographic maps, with any number of subjects and electrodes.

Statistical methods for testing differences between neural images (e.g., PET, MRI or EEG maps) are problematic because they require (1) an untenable assumption of data sphericity and (2) a high subject to electrode ratio. We propose and demonstrate an exact and distribution-free method of significance testing which avoids the sphericity assumption and may be computed for any combination of electrode and subject numbers. While this procedure is rigorously rooted in permutation test theory, it is intuitively comprehensible. The sensitivity of the permutation test to graded changes in dipole location for systematically varying levels of signal/noise ratio, intersubject variability and number of subjects was demonstrated through a simulation of 70 different conditions, generating 5,000 different data sets for each condition. Data sets were simulated from a homogeneous single-shell dipole model. For noise levels commonly encountered in evoked potential studies and for situations where the number of subjects was less than the number of electrodes, the permutation test was very sensitive to a change in dipole location of less than 0.75 cm. This method is especially sensitive to localized changes that would be "washed-out" by more traditional methods of analysis. It is superior to all previous methods of statistical analysis for comparing topographical maps, because the test is exact, there is no assumption of a multivariate normal distribution or of the correlation structure of the data requiring correction, the test can be tailored to the specific experimental hypotheses rather than allowing the statistical tests to limit the experimental design, and there is no limitation on the number of electrodes that can be simultaneously analyzed.

A Study of Multivariate Permutation Tests Which May Replace Hotelling's T2 Test in Prescribed Circumstances.

Multivariate permutation tests are described and studied which may be profitably substituted for Hotelling's one-sample P test in situations commonly arising in behavioral science research. These tests (a) may be computed even when the number of variables exceeds the number of subjects, (b) are distribution-free, (c) may be tailored for sensitivity to specific treatment alternatives, and (d) provide one-sided as well as two-sided tests of hypotheses. Power comparisons were made between the permutation tests and Hotelling's T(2) test under a variety of treatment effect model, correlation structure and number of variables combinations. Results show that the permutation tests have significant power advantages over the T(2) in a variety of circumstances, but may have considerably less power in others.

An alternative method for significance testing of waveform difference potentials.

Guthrie and Buchwald (1991) proposed an ad hoc procedure for assessing the statistical significance of waveform difference potentials that may arise in a variety of psychophysiology research contexts. In our paper, an alternative method is presented and demonstrated that has fewer underlying assumptions than does the Guthrie-Buchwald test and may, therefore, produce better results in some situations. In particular, the test proposed here (a) is distribution free, (b) requires no assumption of an underlying correlation structure (e.g., first-order autoregressive), (c) requires no estimate of the population autocorrelation coefficient, (d) is exact, (e) produces p values for any number of subjects and time points, and (f) is highly intuitive as well as theoretically justifiable. This procedure may be used to carry out multiple comparisons with exact specification of experiment-wise error, however, this test is based on permutation principles and may require large amounts of computer time for its implementation.

"Virtual N400" and slow wave topography to auditory sentence incongruence.

In a simple auditory sentence paradigm, two ERP components were found to be sensitive to violations of sentence congruence: a "virtual N400" and the Slow Wave (SW). Unlike previous studies, the N400 was found to occur very early (peak latency of 250 msec) and have a short duration (196-287 msec), while maintaining the previously described slightly asymmetric right central-parietal negative topography. Because of the early latency, this component was referred to as a "virtual N400." The SW (418-530 msec) was also enhanced and topographically shifted to incongruent sentence terminal words. Its topography consisted of a symmetric frontal minimum and posterior maximum. Although the difference map was also symmetric, a t value map of the congruence effect was maximal over the left posterior temporal area. The very early latency of the "virtual N400" and its decreased duration were produced by a paradigm that allowed for very early recognition of a semantic violation, even before the spoken word was complete. It is postulated that the "virtual N400" indexes word recognition. Semantic processing in indexed by the "virtual N400" as well, but the left posterior temporal asymmetry in the t maps of the Slow Wave may be of even greater import.

The late somatosensory evoked potential in premature and term infants. II. Topography and latency development.

The maturation of latency and scalp voltage topography of the simultaneously bilateral somatosensory evoked potential was studied in 53 neurologically intact pre-term and term infants, from 31 to 40 weeks post-menstrual age. Four peaks (N1, P1, N2 and P2) were reliably identified in all infants. The latency of each peak decreased as the infants matured. Each peak had a unique voltage scalp topography that remained stable as infants matured, even though the maps changed in amplitude intensity. N2 was large, easily identifiable with a central peak, and extremely stable in topography, suggesting that it might be used to evaluate the functional status of the somatosensory cortex in pre-term and term infants who are at high risk for developing intracranial hemorrhage leading to abnormalities of tone and delays in motor development.

The late somatosensory evoked potential in premature and term infants. I. Principal component topography.

Very little is known about the topographic distribution of the cortical somatosensory evoked potential in premature infants. Principal component analysis (PCA) was applied to the wave forms generated from right median nerve stimuli over a relatively long sweep (483 msec post stimulus) at 16 electrodes in 53 infants with postconceptual ages from 31 to 40 weeks, subdivided into 5 groups by 2 week increments. Factor scores were averaged across subjects, within groups and displayed as topographical maps. Four factors accounted for 71-76% of the variance in each of the 5 groups and the factors extracted from the PCA performed independently in each group were markedly consistent. The first factor (N1/P1) had a left posterior minimum and a left frontal-central maximum and probably represents a tangential dipole located in the post-central gyrus. The second factor (N2) was characterized by a consistent left central minimum with a systematic developmental change in the maximum that seemed to imply that its neural generator was changing in orientation as the infants matured. A third factor (N3) accounted for the most variance and appeared to represent the first evidence of activity in the ipsilateral cortex. Finally, a very late fourth factor appeared only in the more mature groups, with uncertain localization. The topographic maps of the factor scores for these 4 factors appear to account for independent generators in the SEP of the premature and term infant.

Topographical and temporal stability of the P300.

Sixteen normal adults listened to a standard oddball auditory paradigm 3 times, each time separated by 15 min, and this protocol was then repeated 1-2 months later. Stability of the wave forms was measured between 250 and 500 msec for each subject and for each of 16 electrodes by the cross-correlation technique described by Glaser and Ruchkin (1976) and Gevins (1987) in which points on 2 digitized wave forms are paired to produce a correlation coefficient. For each subject, the correlation coefficient was generated for each electrode and then averaged across the 2 parietal and 2 central electrodes to produce a single stability measure for the central electrodes, while the cross-correlation coefficients for the 12 remaining electrodes were averaged for a peripheral stability measure. Three-way repeated measures ANOVAs were performed to determine the significance of cross-correlation coefficient differences. The stability over 15 min for the central electrodes was 0.80, indicating that the P300 was very stable over a short time. The peripheral electrodes were significantly less stable than the central electrodes (P = 0.001). The stability of the wave forms was virtually unchanged when assessed over 1 month (P = 0.9). The target wave forms were significantly more stable than the difference waves (target minus non-target) for both the central and peripheral electrodes (P = 0.04 and 0.01). When the 3 blocks within each session were averaged, there was a significant increase in stability (P less than 0.0005). The wave form cross-correlation coefficients can be used as a measure of the stability of a topographical map over time. The map of the target P300 wave form is very stable, showing no loss in stability from 15 min to 1 month, is more stable than the difference wave form and significantly increases in stability when separate trial blocks are averaged together.

The illusion of catch-up growth in premature infants. Use of the growth index and age correction.

Growth data of 61 premature infants who were observed for 29 months were analyzed to determine if there is validity to the concept of catch-up growth. Weight, length, and head circumference were recorded at each visit. For each measurement, a growth index was calculated to facilitate comparison of infants of different ages and sexes. The age of a child at each visit was also corrected for prematurity by subtracting the number of weeks premature from the postnatal chronological age to generate a corrected age. The corrected age was then used to create a corrected growth index for all variables at each visit. Growth data evaluated in the traditional manner (without correction) suggested that catch-up growth occurred. However, growth data for corrected age more closely approximated the growth of full-term children. Graphic impressions were generally substantiated by Hotelling's T2 tests and factorial and one-way repeated-measures analyses of variance with Bonferroni adjustments. The corrected growth data of appropriate-for-gestational-age children approximated normal expected growth, whereas small-for-gestational-age children still demonstrated subnormal growth at 29 months of age, despite correction. In both appropriate-for-gestational-age and small-for-gestational-age children, catch-up growth appears to be a statistical illusion created by charting growth of premature infants using chronological age rather than the more appropriate corrected age. This finding has important implications for the follow-up of premature infants and may affect the diagnostic interpretation of failure to thrive.

A treatment program for failure to thrive: a cost/effectiveness analysis.

Failure to thrive (FTT) is a frequent cause for the admission of infants to the hospital. Such hospitalizations are often lengthy and expensive, and usually do not contribute to an understanding of the etiology of FTT. Generally, organic causes of FTT can be ruled out by a thorough history and physical examination. In this study two groups were examined: 17 infants who were admitted to foster medical placement homes (MPH), private homes with specially trained parents; and a comparison group of 18 infants who were treated in a more traditional way with diagnostic hospitalization. The groups were similar in all regards prior to admission. All infants were less than a year of age. Family disruption was a prominent feature in both groups, but socio-demographic analysis showed them to be similar in all areas studied. The comparison group gained an average of 276 grams in the hospital over 8.6 days. The MPH group gained 362 grams in the hospital over 8.7 days, with an additional 1270 grams in the medical placement home over 31.1 days. Five children were admitted to the medical placement home without hospitalization. After correcting for an expected weight gain of 15 grams per day (normal growth), the comparison group showed a catch-up growth of 16 gms/day, while the MPH group gained 29 gms/day in excess of expectation, almost twice the comparison group. A 100-gram weight gain cost +308 in the MPH program and +1,635 in the traditional approach. This five-fold difference was felt to be a significant deterrent to the continuing approach of admitting children to the hospital for for the workup of FTT.(ABSTRACT TRUNCATED AT 250 WORDS)

A study of risk factor complexes in early adolescent delinquency.

A study was undertaken to document the existence of multiple forms of risk among a sample of 53 delinquents between the ages of 11 and 16 years. When compared with an age-matched comparison group from the same region, the delinquent youngsters were far more likely to show clusters of vulnerability in the areas studied (medical, neurodevelopmental, educational, behavioral, socioeconomic status, family disruption, and cognitive). When cluster analysis was applied to the delinquent group, three subgroups emerged sharing certain traits and accounting for 70% of the cohort. The early identification of so-called risk factor complexes may be helpful in the prevention of delinquency.

Health profiles of early adolescent delinquents.

Comparison of the health status of 53 delinquent and 51 nondelinquent boys revealed that 57 percent of the delinquents, as compared with 20 percent of the nondelinquents, had experienced two or more serious adverse health events (such as hospitalization, loss of consciousness, or an automobile accident). Physical examinations revealed many more conditions requiring intervention in the delinquent than in the nondelinquent boys. Major differences in the two groups' use of health care were apparent: 34 percent of the delinquents either had no medical care or had used only the emergency room, as contrasted with only 8 percent of the nondelinquents. An overall health index that was used to compare the two groups remained statistically significant for a subset of 16 pairs matched on socioeconomic indicators. These results do not imply an etiological link between health status and delinquency, but they do suggest a strong de facto link. The recurrent hospitalizations of the delinquent boys, their substantial use of medications, and their episodic use of health care underscore the importance of an awareness on the part of public health personnel of this group's medical status and of the urgent need for adequately planning the health care of all youngsters in the juvenile justice system.

A study of neurodevelopmental findings in early adolescent delinquents.

Subtle deficits or delays in the development of the central nervous system in young children are associated with problems affecting learning, behavior, and social adjustment. Less is known about the impact of such neurodevelopmental dysfunction in adolescents. This study assesses the possible association between neurodevelopmental delays and juvenile delinquency. An adolescent neurodevelopment examination was devised and administered to 54 delinquents and 51 secondary school students. Six areas were assessed. There were no significant differences in the prevalence of minor neurologic signs (P = 0.37) or in gross motor function (P = 0.02) and temporal sequential organization (P = 0.04). The greatest differences were in visual processing (P = 0.0002) and auditory-language function (P = 0.0001). Eighteen percent of delinquents and 4% of the comparison group were deficient in two or more neurodevelopmental areas. Nine percent of the delinquents and none of the comparison group had three or more dysfunctions. A neurodevelopmental examination may be a useful diagnostic tool for identifying endogenous factors in behavior, learning, and adjustment problems of this age group. Such findings have implications for the formulation of individualized management strategies.