Exploring immediate memory for lists of items by manipulating the inter-item intervals

Psychological time, unlike physical time, is believed to be ‘compressive’ in the sense that the mental representations of a series of events may be internally arranged with ever decreasing inter-event spacing (looking back from the most recently encoded event). If this is true, the record within immediate memory of recent events is severely temporally distorted. Although this notion of temporal distortion of the memory record is captured within some theoretical accounts of human forgetting, notably temporal distinctiveness accounts, the way in which the fundamental nature of the distortion underpins memory and forgetting broadly is barely recognised or at least directly investigated. The intention here was to manipulate the spacing of items for recall in order to ‘reverse’ this supposed natural compression within the encoding of the items. The experimental test of this idea was to compare recall performance using differing schedules of presentation of lists of words (logarithmically expanding, contracting or fixed irregular inter-item spacing). Statistically significant benefits of temporal isolation were observed, with the contracting word series (which we may think of as reversing the natural compression within the mental representation of the word list) showing highest performance (Experiment 1); even when they were controlled for active maintenance processes like attentional refreshing and articulatory rehearsal (Experiment 2 and 3). Further experimental tests suggested that an encoding benefit for the contracting series did not rely simply on providing an opportunity for active verbal maintenance early in the word sequence; for example, the pattern of performance improvement was observed using Chinese characters rather than words (Experiment 4). It was seen that, in addition to temporal isolation of items, a short retention interval (as opposed to no retention interval or a long retention interval) is beneficial for memory (Experiment 5). Finally, benefits of temporal isolation of items were also seen for colour memory (Experiment 6). Additionally, it was seen that benefits of a logarithmically contracting series (in time) were mostly observed only for free recall and not for serial recall. Together the outcomes of the experiments broadly support the notion of temporal compression within the encoding of series of items within immediate memory.