Do Task Cues Influence Memory Strategy Use in Rhesus Macaques?

Background

Memory tasks can be solved either prospectively or retrospectively. Prospective coding means remembering a future response; retrospective coding means remembering a previously seen stimulus. Humans can use either strategy, whereas rhesus macaques have appeared to rely on retrospective coding.

Approach

We cued monkeys toward different strategies using two touchscreen tasks: a match-to-sample (MTS) task and a symbolic, many-to-one (MTO) matching task. To test whether the animals actually used the cues to choose a strategy, we introduced invalid cues on probe trials. If monkeys can flexibly switch coding strategies, invalid cues should produce a greater performance cost on the symbolic matching tests than on the MTS tests.

Findings

Cue validity did not cause a strategy shift. Monkeys did not use cues to decide their memory strategy and appeared to use retrospective coding exclusively in both tasks. Retrospective coding may be the default because maintaining a representation of what was just seen requires less effort than converting a sample to a symbolic match and holding that in mind.

Next steps

A follow-up experiment will use visually similar stimuli to make retrospective coding difficult, pushing monkeys toward a prospective strategy. This tests strategy use through task demands as well as cues, addressing a key limitation of the first experiment. If monkeys remain retrospective even when it is costly, it would suggest that these primates lack the ability to flexibly adopt a prospective strategy on a trial-by-trial basis.