Many of us have had the experience of mentally rehearsing a friend's new phone number, only to dial their old phone number when we try to call them later in the day. This is an example of memory systems interacting. Rehearsing the new phone number relies on working memory, whereas the habit of dialing the old phone number is an example of reference memory. As working memory fades with the passage of time, reference memory takes over.
In a recent paper published in the Journal of Experimental Psychology: Animal Learning and Cognition, Roberts, Strang, and Macpherson (2015) (PDF, 153KB) extend the study of multiple memory systems to pigeons.
Pigeons were first trained in a delayed match-to-sample task in which they were shown a red or green sample stimulus, and then two comparison stimuli (vertical stripes and horizontal stripes). Pigeons were rewarded for selecting vertical stripes after a red sample, and horizontal stripes after a green sample. This task measures working memory: successful performance requires holding the color sample in memory until the comparison stripe stimuli are shown.
Next, pigeons were trained in a visual discrimination task, in which the same vertical and horizontal stripe stimuli were shown, and they were always rewarded for choosing the vertical stripes, and never rewarded for choosing the horizontal stripes. This task establishes reference memory: pigeons develop a habit of choosing the rewarded stimulus.
Critically, in delayed match-to-sample tasks performed after visual discrimination training, there could be a conflict between working and reference memory. When a red patch was shown, the correct response (vertical stripes) was congruent with the habitual response in reference memory (vertical stripes); however, when a green patch was shown, the correct response (horizontal stripes) was incongruent with the habitual response in reference memory (vertical stripes).
There was no difference in performance between congruent and incongruent trials when there was minimal delay between the sample and comparison stimuli, consistent with the use of this task to measure working memory. However, pigeons performed worse on incongruent versus congruent trials when there was a longer delay between sample and comparison stimuli. This suggests that performance relied more on reference memory as working memory was weakened.
Furthermore, differences in performance between congruent and incongruent trials were reduced when working memory was strengthened by increasing the presentation time of the sample stimulus, and when reference memory was weakened by reducing the likelihood of reward in the visual discrimination training (e.g., vertical stripes stimulus rewarded on only 50% of trials). Thus, behavioral performance was determined by the relative strengths of working and reference memory, demonstrating that these systems interact and compete to control behavior.
Independence of working and reference memory was established by analyzing scores based on process dissociation procedures that take into account the relative contributions of working and reference memory to performance on congruent and incongruent trials. Results showed that manipulations that influenced working memory (delay length) did not influence reference memory, and manipulations that influenced reference memory (probability of reward) did not influence working memory.
These results align with those obtained in similar experiments with humans and monkeys, and suggest that working and reference memory are independent, but interactive. Studying and establishing animal models of interactions between memory systems may be useful for developing treatments for human memory impairments, such as memory confusion that characterizes dementia and Alzheimer's disease.
Citation:
Roberts, W. A., Strang, C., & Macpherson, K. (2015). Memory systems interaction in the pigeon: Working and reference memory. Journal of Experimental Psychology: Animal Learning and Cognition, 41(2), 152–162. http://dx.doi.org/10.1037/xan0000053
Note: This article is in the Basic/Experimental Psychology topic area. View more articles in the Basic/Experimental Psychology topic area.