On the heritability of inspection time and its covariance with IQ: a twin study

Using the classical twin design, this study investigates the influence of genetic factors on the large phenotypic variance in inspection time (IT), and whether the well established IT–IQ association can be explained by a common genetic factor. Three hundred ninety pairs of twins (184 monozygotic, MZ; 206 dizygotic, DZ) with a mean age of 16 years participated, and 49 pairs returned approximately 3 months later for retesting. As in many IT studies, the pi figure stimulus was used and IT was estimated from the cumulative normal ogive. IT ranged from 39.4 to 774.1 ms (159±110.1 ms) with faster ITs (by an average of 26.9 ms) found in the retest session from which a reliability of .69 was estimated. Full-scale IQ (FIQ) was assessed by the Multidimensional Aptitude Battery (MAB) and ranged from 79 to 145 (111±13). The phenotypic association between IT and FIQ was confirmed (−.35) and bivariate results showed that a common genetic factor accounted for 36% of the variance in IT and 32% of the variance in FIQ. The maximum likelihood estimate of the genetic correlation was −.63. When performance and verbal IQ (PIQ & VIQ) were analysed with IT, a stronger phenotypic and genetic relationship was found between PIQ and IT than with VIQ. A large part of the IT variance (64%) was accounted for by a unique environmental factor. Further genetic factors were needed to explain the remaining variance in IQ with a small component of unique environmental variance present. The separability of a shared genetic factor influencing IT and IQ from the total genetic variance in IQ suggests that IT affects a specific subcomponent of intelligence rather than a generalised efficiency.     

Evidence of Impaired Glucose Tolerance and Insulin Resistance in Patients With Alzheimer’s Disease

Alzheimer’s disease (AD) and diabetes rarely occur together, a finding that provides a possible clue as to the development of AD. Abnormal glucose metabolism is not limited to diabetes, but also can include impaired glucose tolerance, insulin resistance, and hyperinsulinemia. AD patients have significantly varying insulin levels after drinking sugared sodas and thus may be classified as insulin resistant. After reviewing the literature on impaired glucose tolerance and insulin production in AD, we present several hypotheses as possible explanations for the relationship between insulin resistance and AD. Finally, we suggest future studies, including studies on use of thiazolidinediones (currently used in the treatment of diabetes) in AD.     

Contextual Interference: A Response Planning Account

In two of the three experiments that are reported subjects were trained in either a blocked or a random practice schedule and allowed to self-select the amount of time they used to plan an upcoming movement. According to the reconstruction hypothesis (Lee & Magill, 1985) random practice participants engage greater movement planning processes (i.e. action plan re-construction) during acquisition than do their blocked practice counterparts. It was predicted that such reconstructive activity would be manifest as greater study time being used by random practice subjects as they readied themselves for an imminent response. Data from Experiments 1 and 2 supported this study time prediction while also revealing the typical retention benefit associated with random practice. Interestingly, the acquisition benefit often apparent with blocked practice was not evident when the random practice participants were given sufficient time to plan the upcoming response. These conclusions were supported by data from Experiment 3 that involved a direct manipulation of the amount of study time afforded random and blocked practice participants. Taken together, these data are consistent with the suggestion from the reconstruction hypothesis that more time is necessary for intratrial planning processes during random practice formats. Furthermore, acquisition differences that are commonly observed between high and low contextual interference practice conditions may, at least in part, be associated with the completion of the extra planning processes entertained by random practice participants as the movement is being executed.