Sensory and working memory in a spatial change-detection task by pigeons and humans

Judgements of items viewed less than 100 ms prior are predominantly supported by a sensory, or iconic, memory system. Iconic memory is of high-capacity, but is also volatile and limited in duration. Judgements after longer delays increasingly rely on a working memory system, which is lower in capacity and volatility than sensory memory, but is longer in duration. In four experiments, several factors (e.g., length of delay, number of items, time to view items, presence of a visual mask) were manipulated during a spatial change-detection task conducted with humans and pigeons. Both species were exposed to trials with an array of colored circles (2, 3, and 4 circles in Experiment 1 and 2a; 4, 6, and 8 circles in Experiment 2b) followed by a brief delay (0, 50, and 100 ms in Experiment 1a; 0, 100, and 1000 ms in Experiments 1b and 2), and then were presented with a test display in which the position of one of the items had changed. Pigeons, like humans, were less accurate in selecting the changed item with more items in the display and after longer delays. Pigeons were equally accurate on trials with 0 and 100-ms delays, but worse on trials with a 1000-ms delay; whereas, humans were equally accurate on 100-ms and 1000-ms delays, but better on 0-ms delay trials. Accurate change detection was disrupted in both species when a visual mask was inserted between the sample and test display after a short (100 ms), but not a long (1000 ms) delay. The results support similarity between species in the functional relationships between delay and memory systems, despite time course differences related to sensory memory.