Effects of age on measures of complex working memory span in the beagle dog (Canis familiaris) using two versions of a spatial list learning paradigm

Abstract

The present study used two versions of a spatial list learning (SLL) paradigm to examine the effects of increased cognitive load on visuospatial working memory processes in young and old beagle dogs. In the first experiment, young, and a select group of old dogs were first presented with one item, then two, and then three, and were rewarded for responding to the novel position. The dogs were able to learn the task at short delays, but compared with young dogs, old dogs performed worse at delays of 10 sec, and could not reach longer delays. Analysis of errors indicated that memory was best for end items in the spatial list and that within sessions, the number of errors in later trials was greater than the number of errors in earlier trials. A second version of the task, a modified SLL (mSLL) was developed to control for the use of non-mnemonic strategies on the SLL task. In this version, the first two items were presented individually. Acquisition and maximal memory performance were better in the young relative to the old dogs. Similar to the original SLL design, memory for early list items was worse than memory for later list items in both young and old dogs. The within-session pattern of errors however, did not change from trial to trial on the mSLL. The present results suggest that multiple working memory processes are engaged during complex tests of visuospatial function and the neuroanatomical substrates controlling these processes are affected differentially by age in the beagle dog.

Figure 1

Median number of errors (A) and trials (B) to criterion for each delay of the SLL task for the young and old dogs. No values are shown for the old dogs at delays of 20–20 and 50–20, because only young dogs achieved these longer delays.

Figure 2

Median number of primacy and recency errors for old (A) and young (B) dogs at each delay of the original SLL task. Only one old dog completed criterion measures at the 10-sec delay.

Figure 3

Box-plot of errors as a function of blocks of trials across all sessions of SLL testing at the 5-sec delay for old and young dogs. Median errors for each block of three trials are indicated by a solid line within the box plot. Longer box plots and whiskers indicate greater variability within each group across blocks of trials. Individual data points represent extreme values.

Figure 4

Distribution of total errors on mSLL task. One young male dog (circled) was unable to complete the mSLL task at 5 sec. This young dog was 2-yr older than the oldest young dog and was closer to middle-aged.

Figure 5

Median number of errors (A) and trials (B) to criterion for each delay of the SLL task for the young and old dogs. No values are shown for the old dogs at delays of 20–20 and 50–20, because only young dogs achieved these longer delays.

Figure 6

Median number of primacy and recency errors for old (A) and young (B) dogs on the mSLL task. Errors at the 10-sec delay represent a single old dog. No other old dog completed the 10-sec delay.

Figure 7

Box-plot of errors as a function of blocks of three trials across all sessions of mSLL testing at the 5-sec delay for old and young dogs. Median errors for each block of three trials are indicated by a solid line within the box plot. Longer box-plots and whiskers indicate greater variability within each group across blocks of trials.

Figure 8

An example of a single trial on the original Spatial List Learning (SLL) task. Each trial consists of a series of three phases. In phase one, a single red coffee jar lid occupies one of the three food wells. In phase two, a second identical red lid is placed over one of the two remaining food wells. In the third and final phase of each trial, the last remaining food well is covered with a third identical red lid. Delays for each phase consist of 5–5, 10–10, 20–20, and 50–20 sec. Correct (+) and incorrect (−) positions on each phase are indicated.

Figure 9

An example of a single trial on the modified SLL (mSLL) task. Each trial is composed of a series of three phases. In phase one, a single red coffee jar lid occupies one of the three food wells. In phase two, a second identical red lid is placed over one of the two remaining food wells. During this phase, the first position is not covered by a red lid. In the third and final phase of each trial, the last remaining food well is covered with a third identical red lid, and the first two positions are covered with red lids, but remain unbaited. Delays for each phase consist of 5–5, 10–10, 20–20, and 50–20 sec. Correct (+) and incorrect (−) positions on each phase are indicated.