The role of stimulus comparison in animal perceptual learning: Effects of a distractor placement

Abstract

Research on perceptual learning shows that the way stimuli are presented leads to different outcomes. The intermixed/blocked (I/B) effect is one of these outcomes, and different mechanisms have been proposed to explain it. In human research, it seems that comparison between stimuli is important, and the placement of a distractor between the pre-exposed stimuli interferes with the effect. Results from animal research are usually interpreted in different terms because the type of procedure normally used in animal perceptual learning does not favour comparison. In our experiments, we explore the possibility that a distractor placed between the to-be-discriminated stimuli may interfere with the perceptual learning process in rats. In Experiment 1, two flavoured solutions are presented in an I/B fashion, with a short time lapse between them to favour comparison, showing the typical I/B effect. In Experiment 2, we introduced a distractor in between the solutions, abolishing this effect. Experiment 3 further replicates this by comparing two intermixed groups with or without distractor. The results replicate the findings from human research, suggesting that comparison also plays an important role in animal perceptual learning.

The amount of exposure determines generalization in animal perceptual learning using short inter-stimulus intervals

“…For instance, it is possible that a distractor placed immediately after the second stimulus could interfere with the formation of excitatory connections between both flavours, thus causing the lower generalization observed in Experiment 2. However, we have shown elsewhere (Recio, Iliescu, & de Brugada, 2018) that the presence of this distractor after the presentation of the second compound, either at the end of the morning session (like in Experiment 2) or in the evening session (like in Experiment 1) produced equivalent results, not lending support…”

Perceptual learning after rapidly alternating exposure to taste compounds: Assessment with different indices of generalization.

“…This interpretation also applies to the more conventional test procedure in which generalization to AX is tested after conditioning with BX (e.g., Symonds & Hall, 1995). However, Recio et al (2018) also showed that the effect of rapid alternation (on generalization from Y to AY) was reduced when a distractor (D) was placed between successive presentations of AX and BX during the exposure stage. The distractor had no effect when placed between successive presentations of AX and AX in the group given blocked exposure.…”

“…Recent research has suggested that rapidly alternating and blocked exposure to compounds (AX and BX), principally discriminated by their odors (i.e., A and B; caramel and hazelnut), have different consequences: Alternating exposure increases the capacity of A to interfere with the expression of an aversion to Y relative to blocked exposure (Recio et al, 2018). One interpretation of this effect (and perceptual learning in general) is that alternating exposure to AX and BX results in the salience of A (and B) being higher than after blocked exposure; and that this difference salience affects the ability of A to disrupt the expression of the aversion acquired by Y (e.g., Hall, 2009).…”

“…There is an alternative explanation for the results reported by Recio et al (2018), which derives from the use of odors and the specific test procedure employed. This explanation relies on the possibility that when the presentation of AX and BX are rapidly alternated, the strong odor components (A and B) will not have fully dissipated over the 5-min intervals between AX and BX.…”

Some unresolved issues in perceptual learning.

“…It seems, therefore, to drive a wedge between these studies and the effects obtained with animal subjects, where, as we have seen, evidence for a comparison process is not strong. It is of special interest, therefore, that recent experiments by Recio, Iliescu, and de Brugada (2018) have provided some evidence of a distractor effect using rats trained in a flavor-aversion procedure. In the first of their experiments, rats were given preexposure with closely spaced presentations of the compound flavors AX and BX, the 5-min gap between the stimuli being filled simply by access to water.…”