Electronic Theses and Dissertations

Date of Award


Document Type


Degree Name

Ph.D. in Psychology

First Advisor

Karen E. Sabol

Second Advisor

Kenneth Sufka

Third Advisor

Nick Prins

Relational Format



Attention Deficit-Hyperactivity Disorder (ADHD) is currently the neurodevelopmental disorder most commonly diagnosed in children in the United States, and one of the defining characteristics of ADHD is inattention. Inattention is marked by increased lapses in attention, and when assessed clinically, it has been highly correlated with reaction-time variability (RTV). Evidence from the human/clinical literature has shown an inherently higher RTV to be the primary quantitative indicator of an ADHD diagnosis. Reaction-time distributions are characterized by an asymmetrical rightward skew, and because of the prevalence of this presentation, it has been theorized that the distribution peak and skew represent separate phenomena, or attention and lapses in attention respectively. By separating out the motor component of reaction time and employing parameters that closely parallel those used in clinical assessments of attention, the two-choice serial reaction time task (2-CSRTT) yields a measure in rodents, initiation time (IT), akin to human reaction time. Similar to the analysis of human reaction time using an ex-Gaussian approach, the peak and skew of IT distributions can be dissociated and separately analyzed using the mode and deviation from mode (distribution mean minus the mode), thus rendering a rodent variability measure indicative of lapses in attention. The effects of attentional stress are cumulative and can be induced via manipulations of both environmental and external factors. The current studies utilized both by decreasing signal salience and blocking the neurotransmitter, acetylcholine. Additionally, in order to separate high performing rats from low performers, a median split based on training IT devmode was introduced as a third independent variable. Lapses significantly increased when salience was reduced but remained unaffected by scopolamine HBr for all rats, as no main effect of baseline performance was observed following the median split. However, a three-way interaction effect was observed and under less salient conditions, lapses in attention increased for low performing rats following the blockade of acetylcholine transmission. The current findings, therefore, implicate acetylcholine in the facilitation and regulation of higher order attentional processes, such as sustaining attention and maintaining vigilance, and indicate an increased sensitivity to attentional stress in low performers.



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