“Time Present and Time Past”*
This chapter is concerned the mechanisms in pigeons that underlie the short-term retention of information about the duration of events. It discusses the initial observations that suggested a foreshortening process in pigeons' short-term memory for duration and then describe the Subjective Shortening model of pigeons' memory for time that was proposed to describe this process. The chapter also discusses results that appear to confirm certain assumptions of this model, as well as results that have indicated that the processes underlying a pigeon's memory for time are more complex than assumed by this preliminary model. The initial observations that suggested the occurrence of a foreshortening process in pigeons' memory for time were obtained inadvertently during the course of research on pigeons' discrimination and memory for events that were assumed to differ in biological significance. The assumption that systematic errors in pigeons' memory for time arise because of discrepancies between working and reference memory has received strong support.