L. Cohen et S. Dehaene, COMPETITION BETWEEN PAST AND PRESENT - ASSESSMENT AND INTERPRETATION OF VERBAL PERSEVERATIONS, Brain (Print), 121, 1998, pp. 1641-1659
Perseveration consists of the inappropriate repetition of a preceding
behaviour when a new adapted response is expected. We have developed s
tatistical tools that make it possible to reveal such perseverations,
assess their significance and study their finer characteristics, such
as their temporal course and impaired processing level, This approach
is illustrated and evaluated through analyses of naming errors produce
d by three patients with impairments affecting different stages of the
processing chain leading from visual perception to speech production.
These examples of perseverations include the intrusion not only of wh
ole words (patient R.A.V.) but also of isolated phonemes (patient D.U.
M.) or of visual features (patient Y.M.) from previous trials. Zn all
cases, the probability that an error is a perseveration from a previou
s trial is an exponentially decreasing function of the lag between the
two trials considered. This suggests that perseverations reflect a de
caying internal variable, such as an internal level of activation of p
revious utterances, Based on these empirical results, we put forward a
tentative mechanism for the generation of perseverations: whenever a
given processing level is deprived of its normal input, persistent act
ivity inherited from previous trials is no longer overcome by current
input, and is revealed in the form of perseverations.