Reconstructing the recent visual past: Hierarchical knowledge-based effects in visual working memory.

This paper presents two experiments that examine the influence of multiple levels of knowledge on visual working memory (VWM). Experiment 1 focused on memory for faces. Faces were selected from continua that were constructed by morphing two face photographs in 100 steps; half of the continua morphed a famous face into an unfamiliar one, while the other half used two unfamiliar faces. Participants studied six sequentially presented faces each from a different continuum, and at test they had to locate one of these within its continuum. Experiment 2 examined immediate memory for object sizes. On each trial, six images were shown; these were either all vegetables or all random shapes. Immediately after each list, one item was presented again, in a new random size, and participants reproduced its studied size. Results suggested that two levels of knowledge influenced VWM. First, there was an overall central-tendency bias whereby items were remembered as being closer to the overall average or central tokens (averaged across items and trials) than they actually were. Second, when object knowledge was available for the to-be-remembered items (i.e., famous face or typical size of a vegetable) a further bias was introduced in responses. The results extend the findings of Hemmer and Steyvers (Psychonomic Bulletin & Review, 16, 80-87, 2009a) from episodic memory to VWM and contribute to the growing literature which illustrates the complexity and flexibility of the representations subtending VWM performance (e.g., Bae, Olkkonen, Allred, & Flombaum, Journal of Experimental Psychology: General, 144(4):744-63, 2015).

Raising argument strength using negative evidence: a constraint on models of induction.

Both intuitively, and according to similarity-based theories of induction, relevant evidence raises argument strength when it is positive and lowers it when it is negative. In three experiments, we tested the hypothesis that argument strength can actually increase when negative evidence is introduced. Two kinds of argument were compared through forced choice or sequential evaluation: single positive arguments (e.g., "Shostakovich's music causes alpha waves in the brain; therefore, Bach's music causes alpha waves in the brain") and double mixed arguments (e.g., "Shostakovich's music causes alpha waves in the brain, X's music DOES NOT; therefore, Bach's music causes alpha waves in the brain"). Negative evidence in the second premise lowered credence when it applied to an item X from the same subcategory (e.g., Haydn) and raised it when it applied to a different subcategory (e.g., AC/DC). The results constitute a new constraint on models of induction.

On domain differences in categorization and context variety.

Membership in many natural categories is considered all-or-none, while membership in most artifact categories is found to be graded. We introduce an alternative for the prevailing view that this domain difference in categorization results from representational differences. The context variety account posits that an item's gradedness reflects the variety of contexts it appears in. Items that feature in a variety of contexts are assumed to be more likely to elicit a graded categorization response, since the suggested target category only provides one of many solutions to the question of the item's identity. We review earlier work that suggested a domain difference in context variety, with artifactual items appearing in a greater variety of contexts than natural ones. The context variety domain difference is established in two separate experiments but is shown not to explain the domain difference in categorization. A selection of artifactual and natural items, for which the domain difference in context variety is reversed, is presented for categorization in a third experiment. This selection, too, fails to provide evidence for the context variety account of categorization differences. The domain difference in categorization is shown to be robust against this manipulation. Context variety appears to have no bearing on categorization, so the context variety account is not a sustainable alternative to accounts that posit representational differences between natural and artifact categories.

Feature integration in natural language concepts.

Two experiments measured the joint influence of three key sets of semantic features on the frequency with which artifacts (Experiment 1) or plants and creatures (Experiment 2) were categorized in familiar categories. For artifacts, current function outweighed both originally intended function and current appearance. For biological kinds, appearance and behavior, an inner biological function, and appearance and behavior of offspring all had similarly strong effects on categorization. The data were analyzed to determine whether an independent cue model or an interactive model best accounted for how the effects of the three feature sets combined. Feature integration was found to be additive for artifacts but interactive for biological kinds. In keeping with this, membership in contrasting artifact categories tended to be superadditive, indicating overlapping categories, whereas for biological kinds, it was subadditive, indicating conceptual gaps between categories. It is argued that the results underline a key domain difference between artifact and biological concepts.