Aktuelle Neurologie 2005; 32 - P310
DOI: 10.1055/s-2005-919344

The Mental Clock Test and its asymmetry

J Kukolja 1, J.C Marshall 1, G.R Fink 1
  • 1Aachen; Oxford, UK

The Mental Clock Test is a standardised procedure to test for hemineglect in visual imagery.

Patients with representational neglect show longer reaction times (RT) and higher error rates (ER) in the left (LHF) than in the right imagined hemifield (RHF). In a recent study we found that also healthy subjects show a similar pattern of RT and ER. The aim of the present study was to further investigate this imagery dependent hemifield asymmetry of the Mental Clock Test by comparing two different types of stimulus presentation in both normals and patients with neglect.

Subjects listened to spoken clock times and then judged whether the angle between the clock hands was > or <90°. Both clock hands were either positioned in the LHF or the RHF of the clock face. The clock times were presented either in a 'digital' (e.g. 'eight fifty') or in a 'common speech' manner (e.g. 'ten to nine'). 12 healthy right handed volunteers and 8 patients with chronic neglect after right hemisphere damage took part in the study.

Healthy subjects showed an interaction of stimulus presentation and hemifield: In the digital condition, subjects showed significantly longer RT and higher ER in the LHF than in the RHF. In the common speech condition, there was no significant RT or ER difference between visual hemifields. 4 patients with only slight residual neglect showed a pattern of RT and ER similar to that of healthy subjects. 1 patient with severe chronic neglect showed signs of representational neglect (longer RT and higher ER in the right hemifield in both the digital and common speech condition). 3 patients were excluded due to high ER.

The first experiment reproduced the results of our previous study, showing a directionality or asymmetry implicit in the classic Mental Clock task due to either increasing numbers from right to left on the clock face or clockwise mental rotation as a strategy to solve the task. Using 'common speech' overcomes this issue. Despite the limited number of patients the study indicates that only more severe impairment induced representational neglect.