Measurement & Analysis of the Temporal Discrimination Threshold Applied to Cervical Dystonia

Summary

Methods for the measurement and analysis of the temporal discrimination threshold are presented, and its application to the study of the pathogenesis of cervical dystonia are discussed.

Abstract

The temporal discrimination threshold (TDT) is the shortest time interval at which an observer can discriminate two sequential stimuli as being asynchronous (typically 30-50 ms). It has been shown to be abnormal (prolonged) in neurological disorders, including cervical dystonia, a phenotype of adult onset idiopathic isolated focal dystonia. The TDT is a quantitative measure of the ability to perceive rapid changes in the environment and is considered indicative of the behavior of the visual neurons in the superior colliculus, a key node in covert attentional orienting. This article sets out methods for measuring the TDT (including two hardware options and two modes of stimuli presentation). We also explore two approaches of data analysis and TDT calculation. The application of the assessment of temporal discrimination to the understanding of the pathogenesis of cervical dystonia and adult onset idiopathic isolated focal dystonia is also discussed.

Introduction

Temporal discrimination describes a person's ability to discriminate, or perceive, rapid changes in their environment. The temporal discrimination threshold (TDT) is the shortest time interval at which an individual can perceive that two sequential sensory stimuli are asynchronous. Temporal discrimination has been shown to be abnormally prolonged in disorders affecting the basal ganglia, including dystonia^{1,2,3,4,5,6,7}.

Protocol

The Medical Research Ethics Committee at St. Vincent's University Hospital, Dublin gave approval for the recruitment of patients with cervical dystonia, their siblings (unaffected by dystonia), and healthy controls, to participate in the protocol described below.

1. Hardware & Software Solutions

Note: Two hardware options have been developed to display visual stimuli with precise inter-stimulus intervals. Both were designed and built in-house at the Trinity Centre for Bioengineering, Trinity College Dublin, and have been previously described^5,16. Th....

Results

Examples of filled score sheets are provided in Tables 1 and 2, where these respectively represent results following staircase and random stimulus presentation methods. The thresholds for each run (the timing of the first of three stimulus pairs deemed to be 'different'), are highlighted. In the case of Table 1, the TDT is calculated as 25 ms (i.e., the median of 40, 25, 25, 25, 45, 25, 40, 10 ms). These data are.......

Discussion

TDT Measurement and Analysis

Two forms of apparatus (table-top and headset), two methods of stimulus presentation (staircase and random), and two approaches to data analysis (traditional and distribution) have been presented to illustrate how to measure and quantify a person's temporal discrimination ability. The portable headset provides a convenient hardware option that ensures consistency in distance and angles between the participant and the LED light sources while al.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
TDT head set	Can be supplied by Trinity Centre for Bioengineering, Trinity College Dublin.  Alternatively full instructions are available for free download from http://www.dystoniaresearch.ie/temporal-discrimination-threshold/	1	A custom-built, portable device for the presentation of visual stimuli.
TDT table top LED box	Can be supplied by Trinity Centre for Bioengineering, Trinity College Dublin.  Alternatively full instructions are available for free download from http://www.dystoniaresearch.ie/temporal-discrimination-threshold/	2	A custom-built, table-top device for the presentation of visual stimuli.
Microcontroller	Can be supplied by Trinity Centre for Bioengineering, Trinity College Dublin.  Alternatively full instructions are available for free download from http://www.dystoniaresearch.ie/temporal-discrimination-threshold/	3	A custom-built microcontroller for the delivery of visual stimuli in staircase or random order, with precise inter-stimulus intervals.