DISCRIMINATION IN DYSTONIA: TIME FOR A RETHINK?

<jats:sec><jats:title>Introduction</jats:title><jats:p>Abnormal temporal discrimination thresholds (TDT) are thought to reflect abnormal temporal processing in dystonia. Despite widespread use of the TDT paradigm the task has been developed little since its inception; even though current paradigms may test additional factors unrelated to temporal processing.</jats:p></jats:sec><jats:sec><jats:title>Method</jats:title><jats:p>22 healthy subjects and 22 subjects with cervical dystonia (CD) were tested with two novel tasks. The first task ‘gap detection’ was a forced choice version of the TDT. Complicating spatial elements of the paradigm were removed and modelling data psychophysically increased the dimensionality of analysis informing on task performance. The second task ‘interval discrimination’ tested the ability to classify the length of two successive intervals.</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>Gap detection Equality of performance between groups was seen for general markers of performance such as hit rate, false positive rate and modelled psychometric function parameters. However, subjects with CD were significantly slower to make decisions. Interval discrimination No difference in the sensitivity between groups to classify differences in intervals was seen.</jats:p></jats:sec><jats:sec><jats:title>Conclusions</jats:title><jats:p>These results are surprising and challenge currently held concepts about the significance of previously documented abnormalities of TDTs in which a simple timing deficit is widely assumed. We hope that the ensuing discussion re-invigorates work to define the true biological correlate of TDT anomalies in dystonia as this will provide critical insight into its pathogenesis.</jats:p></jats:sec>