Differential Modulation of Clock Speed by the Administration of Intermittent Versus Continuous Cocaine.

The roles that psychostimulant sensitization and tolerance play in temporal perception in the seconds-to-minutes range were assessed in rats. Cocaine (20 mg/kg/day) was administered for 2 weeks either intermittently via daily injections (induces sensitization) or continuously via an osmotic minipump (induces tolerance). Interval timing was evaluated throughout administration and withdrawal. Injections of cocaine caused immediate, proportional, leftward shifts in peak times, indicating an increase in the speed of an internal clock. These shifts grew progressively larger with repeated administration, indicating that stimulant-induced increases in clock speed can be sensitized. Continuous cocaine administration produced no reliable effects. These results suggest that the mechanisms of sensitization may play a considerable role in drug-induced alterations of the perception of time. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

When Is the Ball Going to Hit the Ground? Duration Estimates, Eye Movements, and Mental Imagery of Object Motion.

Performance in 2 versions of a computer-animated task was compared. Participants either indicated the time of arrival of a target that rolled off a horizontal surface and fell--hidden from view--onto a landing point (production task) or judged flight time on a rating scale (judgment task). As predicted, performance was significantly better in the production task (Experiment 1), in which imagery of object motion probably replaced reasoning processes. Participants who exhibited eye movements suggesting mental tracking performed particularly well in the production task (Experimenl 2). There was, however, no decrement in performance when participants were asked to fixate the point where the target disappeared. For motion duration estimations, eye movements seem to be only a by-product of mental tracking. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of the Fragile X Status Categories and the Fragile X Mental Retardation Protein Levels on Executive Functioning in Males and Females With Fragile X.

The effects of a fragile X disorder on executive function impairment were assessed in 144 extended families, which included individuals with fragile X premutation and full mutation and their relatives without fragile X. A modification of the maximum-likelihood estimators for pedigree data, as well as ordinal logistic regression, were used in data analysis. The most outstanding deficit, occurring especially in males, involved impaired capacity to use an intention to regulate purposeful behavior. This deficit occurred independently of general cognitive impairment but was related to depletion of fragile X mental retardation 1 gene protein product. The other executive function deficits were accounted for by the general cognitive impairment. Possible mechanisms of the effect of fragile X premutation on impairments of executive functioning are considered. (PsycINFO Database Record (c) 2010 APA, all rights reserved)