Location and salience of unique features in human perceptual learning.

Abstract

Preexposure to intermixed presentations of a pair of similar stimuli (AX and BX, where A and B represent distinctive features, and X the features the stimuli hold in common) facilitates subsequent discrimination between them. This perceptual learning effect has been interpreted as indicating that the loss of effective salience resulting from repeated presentation of a stimulus is attenuated or reversed by a salience-modulation process that operates on the unique stimulus features A and B during intermixed preexposure. In 3 experiments, we examined discrimination after intermixed preexposure to AX and BX, making comparison with a condition in which novel unique features were added to the preexposed background (CX and DX). In all experiments, we also monitored eye gaze during both preexposure and the test. Experiments 1 and 2 found discrimination of the preexposed stimuli to be superior. This result cannot be explained by salience-modulation theories that suppose that intermixed preexposure merely attenuates loss of salience to the unique features A and B; it suggests, rather, that intermixed preexposure to AX and BX enhances the salience of, or attention paid to, the distinctive features. Experiment 3 demonstrated that exposure increases sensitivity to the spatial location of the features, a conclusion confirmed by analysis of eye gaze.

Perceptual learning with complex visual stimuli is based on location, rather than content, of discriminating features.

“…The current results (as with those of Wang et al, 2012) directly question the theoretical interpretation of all other studies using the same type of checkerboard stimulus. Moreover, the current results provides concrete evidence that implicitly reinforced attentional mechanisms can contribute to the effects of exposure on discrimination performance, and thus that such mechanisms must be considered in all studies of human perceptual learning.…”

“…Indeed, Wang and Mitchell (2011) have clearly demonstrated that participants look to the location where exposed unique features appear -even when those features are absent on a given trial. Moreover, in Experiment 3 of Wang et al (2012) this tendency to look at the location where the exposed features appeared was maintained even when novel features appeared in those places. However, while providing evidence that participants have learnt the location of the unique features of the exposed stimuli, examining gaze direction in this manner does not assess whether they have genuinely learnt nothing about the content of those features at all.…”

“…This is certainly consistent with the idea that subjects learn more about location than content, but, again, it does not directly assess whether there was no content-based learning at all. One reason for this is that there was no analysis in Wang et al (2012) of whether the absence of a significant effect of content exposure genuinely supports the absence of such an effect (such as using the Bayes factor analysis as described here).…”

“…More importantly, in Wang et al (2012) participants received a single test-phase involving trials where the exposed features A/B appear in the trained locations or in a new location, while novel features C/D appear either in the trained location for A/B or in a new location.…”

“…More recently, in Experiment 3 of Wang et al (2012) it was found that after exposure to AX and BX, eye gaze during test is directed to the location at which A and B appeared during training, regardless of whether the exposed features A and B, or novel features C and D, were present at these locations. Moreover, discrimination performance with both novel and exposed features was better when they appeared at the location at which A and B were presented during initial exposure than when they appeared elsewhere.…”