Titrating DMTS with a Dementia Patient

Delayed matching-to-sample (DMTS) procedures have often been used when studying what is generally known as short-term memory. The sample stimulus is presented, and then it is removed for n seconds at the onset of the comparison stimuli. The delay can either be changed by the experimenter from one condition to the next (fixed DMTS), or it can change as a function of the participants performance, increasing as with correct responses and decreasing with incorrect responses (titrating DMTS). In the present experiment, the titrating DMTS procedure was used to study how much the delay could be stretched in a patient diagnosed with dementia. The participant did not get instruction about looking for similarities to begin with so that behavior could be described in terms of conditional discrimination. In the first titration phase, starting with 0s delay, the participant did not respond in accordance with the identity of the stimuli. An errorless learning phase with 0s delay did not increase number of correct responses above chance level and nor simultaneous matching. Therefore, we introduced specific instruction stating that the participant was required to “choose the identical one” and started the titration again from 0 s delay. The results showed that after introducing the instruction the participant responded in accordance to the identity of the stimuli and they delay increased to up to 3000ms. Future experiments could 1) compare the use of fixed DMTS vs. titrating DMTS within participants and 2) teach pre-current behavior to increase the length of the delay when using titrating DMTS.