Behavioral Variability: Implications for Rehabilitation John Whyte, MD, PhD Moss Rehabilitation Research Institute & Thomas Jefferson University

Clinical Case Examples Minimally conscious state – High variability in response rate and accuracy rate in command following and yes/no communication – Occasional dramatic cases of variability Apraxia of speech – The patient does not lack the absolute capacity to produce specific speech sounds; they lack the ability to do so reliably

Treatment Implications How much assessment does it take to characterize a patient’s current status or response to treatment? How much safe performance guarantees safety after discharge? Are there ways to work on consistency of performance other than working on overall quality of performance?

Research Examples In our attention studies, central tendency of RT is strongly correlated with measures of dispersion in both patients and controls. Transformations that are intended to eliminate this intrinsic correlation work poorly (either a positive correlation remains or becomes negative). We’ve found it difficult to isolate a variability parameter and be confident it was not a statistical artifact.

Big Question #1 Are we sure there is an independent phenomenon of a “variability deficit” vs. an intrinsic relationship between variability and central tendency?

Big Question #2: What would constitute evidence for a separable impairment in “behavioral consistency”? – Ability to match subjects on central tendency (a thorny issue in itself) but find differences in variability? – Different neuroanatomic correlates for central tendency and variability? – Differential treatment responsiveness?