Overshadowing by fixed- and variable-duration stimuli

Abstract

Two experiments investigated the effect of the temporal distribution form of a stimulus on its ability to produce an overshadowing effect. The overshadowing stimuli were either of the same duration on every trial, or of a variable duration drawn from an exponential distribution with the same mean duration as that of the fixed stimulus. Both experiments provided evidence that a variable duration stimulus was less effective than a fixed duration cue at overshadowing conditioning to a target CS; moreover, this effect was independent of whether the overshadowed CS was fixed or variable. The findings presented here are consistent with the idea that the strength of the association between CS and US is, in part, determined by the temporal distribution form of the CS. These results are discussed in terms of time-accumulation and trial-based theories of conditioning and timing.

The effects of stimulus distribution form during trace conditioning

“…For example, it might for some reason have been easier to respond during a fixed-duration CS; however, we observed higher levels of responding to a cue trained with a fixed duration even when the animals were tested under identical conditions (Jennings et al, 2013). Furthermore, we also demonstrated that fixed-duration cues produce better overshadowing and better blocking than their variable counterparts (Bonardi, Mondragón, Brilot & Jennings, 2015; Jennings & Bonardi, 2017). Conditioning theories would interpret these findings as evidence that fixed-duration cues acquire more associative strength than variable CSs.…”

“…Experiments 1 and 2 examined learning in a trace conditioning task, in which the CS was fixed, but the trace interval was either fixed or variable. In experiments using delay conditioning, we have observed higher levels of responding during a CS that is fixed than during one that is variable (Bonardi et al, 2015; Jennings et al, 2013; Jennings & Bonardi, 2017). We have argued here that this could either be due to the temporal distribution of the CS per se or to the fact that CS onset was only informative with respect to the time of food delivery in the fixed case.…”

Blocking by Fixed and Variable Stimuli: Effects of Stimulus Distribution on Blocking

“…Even under equivalent testing conditions, fixed-duration cues elicited higher levels of responding than variable-duration cues of the same mean duration. In a later study Bonardi et al (2014) found that overshadowing was more profound when the overshadowing cue was fixed duration than when it was variable.…”

Cue duration determines response rate but not rate of acquisition of Pavlovian conditioning in mice

“…This approach has been used by others (e.g., Holland, 2000 ). An alternative approach to test the strength of learning, independent from performance effects, has been to assess the ability of the cues to restrict learning with other cues ( Bonardi et al, 2015 ; Jennings & Bonardi, 2017 ). For example, if cues differ in their strength of learning, then they should differ in their ability to block the acquisition or expression of conditioned responding with new cues.…”