A longer retention interval increases subjective similarity

High subjective similarity frequently associates with poor retention. Thus, a longer retention interval may increase subjective similarity as well as worsen retention. To investigate this hypothesis, college students made same-different discriminations for two lines that were the same or different in length with intervals between them of 414 or 3314 ms. A corresponding experiment used tones and frequency. For both experiments, the longer interval produced the poorer overall performance (i.e., retention). This outcome stemmed more from a poorer performance on different stimuli than on same stimuli. This type of interaction implies a higher subjective similarity. So, the longer interval both increased subjective similarity and worsened retention, as hypothesized.