The nature of the task stimuli affects graphic perseveration severity: Insights from a single case study

Graphic perseveration in target-cancellation tasks has been frequently described in patients with right brain damage and unilateral spatial neglect. Conversely, among patients with dementia, the spontaneous production of complex graphic perseverations, as well as their triggers and modulating factors, have been poorly understood. Here we describe the case of RM, a patient with Alzheimer's dementia, who produced a rich pattern of complex graphic perseverations at target-cancellation tasks, especially with abstract target stimuli, i.e., lines.

We developed an ad-hoc behavioral paradigm to investigate patient RM's performance at two versions of a target-cancellation task: fork-cancellation and line-cancellation. In both versions, RM was asked to cross the blue targets, while crossing a red target was considered a false alarm, as a proxy of incorrect response inhibition capacity. Moreover, we classified the presence and intensity of two other graphic perseverative behaviors, i.e., additional marks and scribble perseveration.

Complex graphic perseverations and false alarms were more frequent in the line-compared to the fork-cancellation trials. Conversely, the semantic nature of the task did not differentially modulate the occurrence of additional marks and scribble perseverations.

We argue that the breakdown of RM's executive functioning at the semantic-representational level was a prerequisite for such complex graphic perseverations to occur. Furthermore, we provide hints on the potential modulatory effects of stimulus concreteness on the expression of such complex productive behavior.