Unsupervised category learning with integral-dimension stimuli

Abstract

Despite the recent surge in research on unsupervised category learning, the majority of studies have focused on unconstrained tasks in which no instructions are provided about the underlying category structure. Relatively little research has focused on constrained tasks in which the goal is to learn predefined stimulus clusters in the absence of feedback. The few studies that have addressed this issue have focused almost exclusively on stimuli for which it is relatively easy to attend selectively to the component dimensions (i.e., separable dimensions). In the present study, we investigated the ability of participants to learn categories constructed from stimuli for which it is difficult, if not impossible, to attend selectively to the component dimensions (i.e., integral dimensions). The experiments demonstrate that individuals are capable of learning categories constructed from the integral dimensions of brightness and saturation, but this ability is generally limited to category structures requiring selective attention to brightness. As might be expected with integral dimensions, participants were often able to integrate brightness and saturation information in the absence of feedback--an ability not observed in previous studies with separable dimensions. Even so, there was a bias to weight brightness more heavily than saturation in the categorization process, suggesting a weak form of selective attention to brightness. These data present an important challenge for the development of models of unsupervised category learning.

Categorization training increases the perceptual separability of novel dimensions

“…There is a large body of evidence suggesting that the one-dimensional categorization task is learned through a rule-based categorization system, whereas the information-integration task is learned through a separate procedural categorization system (for reviews, see Ashby & Maddox, 2005;Ashby & Valentin, 2005). On the other hand, when stimuli vary along integral dimensions, a one-dimensional task is not consistently easier to learn than an informationintegration task (Ell et al, 2012).…”

“…On the other hand, when stimuli vary along integral dimensions, people show limited ability to learn unsupervised categories and they do not show a strong preference for one-dimensional rules. Instead, they show a variety of strategies, including integration of information from both dimensions (Ell, Ashby, & Hutchinson, 2012).…”

Evaluation of omission testing as a method for identifying important odorants in a mixture

“…Furthermore, according to Soto and Ashby's () research on category learning, the process of storing odor activity patterns in memory is implicit. One strategy that has been shown to help such implicit learning involves training participants by exposing them to the odor mixtures of interest and providing immediate feedback on the correctness of their responses (Ell et al, ). The participants in our study had no prior exposure to the full five‐compound mixture or any of the mixtures with one of the five compounds removed.…”

“…Instructions and responses were communicated using SIMS Sensory Software on computers in sensory booths. We used A‐not‐A tests throughout these sessions because Ell, Ashby, and Hutchinson () demonstrated that providing immediate feedback on the correctness of such yes/no decisions enhanced implicit learning of categories. Providing immediate feedback after the single sniff and response to the A‐Not‐A test seemed more efficient for promoting learning of “A” than providing feedback after the set of three sniffs required for the more commonly used triangle test.…”

The time course of explicit and implicit categorization

“…They show that response deadlines selectively impair II category learning and trained II categorization. Others have shown that II category learning is selectively impaired if feedback on categorization trials is delayed for a few seconds (Maddox et al, 2003; Maddox & Ing, 2005), if category learning is unsupervised (Ashby, Queller & Berretty, 1999; Ell, Ashby & Hutchinson, 2012), or if category knowledge is imparted observationally and not through trial-based reinforcement (Ashby, Maddox & Bohil, 2002). These results support the idea described above that II category learning is served by a cascade of temporally organized (and temporally inflexible) events that surround the reinforcement-mediated strengthening of dopamine-related synapses (Ashby et al, 2007).…”