On Rate-Sensitive Habituation

The responses elicited by many stimuli diminish in strength with repeated stimulus presentation (habituation). This property is consistent with models in which short-term memory for recent stimuli suppresses the current response. Habituation also depends on stimulus spacing: It occurs more rapidly when interstimulus intervals (ISIs) are short than when they are long, but also recovers more rapidly after short ISIs (rate sensitivity). The effect of ISI on habituation rate is consistent with a simple one-stage process, but the effect of ISI on recovery rate seems to require a serial process in which two or more habituating units are cascaded, with earlier (peripheral) units in the series having shorter time constants than later (central) units. Rate-sensitive habituation may underlie puzzling effects of reinforcement learning such as the partial-reinforcement and successive-contrast effects.