Performance inconsistency in the ovine delayed-match-to -sample task

Sheep can perform a wide range of cognitive tasks (intra-dimensional extra-dimensional set shifting task, stop-signal task, facial recognition task) indicative of high level learning and memory attributes. The delayed-match-to-sample (DMS) task involves the presentation and removal of a reference image, a delay followed by the presentation of two or more sample images. The task requires memory of the sample image to be matched to the reference image with the task becoming more cognitively demanding the greater the delay. Fourteen female sheep, previously trained on an automated operant system were used for this study. The DMS task used two sample images (S+, S-) and the delay between the reference and the sample images was set at 3 seconds. All sheep reached the success criteria (eight out of ten trials/ six consecutive trials) but none could sustain this performance level for more than 2 sessions. The reasons for performance inconsistency are discussed.