Durbin and Stergiedis in Cognitive Brown Bag Weds. 5/3 at noon

There will be two First Year Project Reports, by Jeffery Durbin and Dimitris Stergiedis, in the Cognitive Bag Lunch on Wednesday May 3 at 12pm in Tobin 521B. Titles and abstracts below. All are welcome!

Presenter: Jeffery Durbin

Tile: Characterizing the Visuospatial Sketchpad: Rehearsal and Retrieval in Visual Short-Term Memory

Abstract: Sternberg’s (1966) classic short-term memory task produces a pattern of reaction times (RTs) suggestive of serial exhaustive search through memory when subjects are given ample time to encode the memory set items and establish a rehearsal sequence. However, if the memory set items are presented quickly, RTs and accuracy reveal a parallel search process with a strong recency gradient (i.e., recently studied items are recognized more quickly and accurately). These phenomena have been well described for verbal material, but few studies have addressed the dynamics of rehearsal and search for purely visuospatial information and no studies have examined RTs following slow sequential presentation of the memory set. To address whether sequential rehearsal occurs for visuospatial information, we developed a novel visuospatial short-term memory task in which participants saw a sequence of colored dots (500 ms per dot) along a horizontal line and, after a brief delay (500 ms mask), gave a binary “old” / “new” response to a single test item. We compared four versions of the task, which varied in how similar the lures were to the items in the study sequence: lures were either a recombination of a previously viewed color and location (both old), a new color in an old location (new color), an old color in a new location (new location), or a new color in a new location (both new). Neither RTs nor accuracy revealed a pattern indicative of serial search in any of these conditions, suggesting a lack of sequential rehearsal. A recency gradient was observed for conditions in which color information was necessary (new color, both old), with negligible set size effects across the gradient. In contrast, the recency gradient was reduced for conditions where location information could serve as the sole dimension of evaluation (new location, both new), and set size effects were seen at each level of recency. These findings suggest that color information suffers from strong retroactive interference such that previous color representations are “overwritten,” whereas location representations are blurred with each presentation, as if the location information has been “averaged.”

Presenter: Dimitris Stergiedis

Title: Does providing a subtle reasoning hint remedy the conjunction fallacy?

Abstract: Humans are in general poor at making judgments that adhere to the logical principles of probability theory. One demonstration of this is termed the “conjunction fallacy”: judging a conjunction (A&B) as being more probable than its constituent (A). Systematic commitment of the conjunction fallacy has been shown in numerous studies on probability judgments. Different actions to remedy the fallacy have been suggested. According to the nested-sets hypothesis, when the nested-set structure of a problem becomes clear (i.e. the relation between categories and subcategories), then the conjunction fallacy is remedied. However, previous demonstrations of this remediation have provided very explicit task-related information and it can be questioned whether it is trivial that such information leads to more correct judgments. The primary aim of this study was to test the nested-sets hypothesis in two different formats of a probability judgment task, by more subtly hinting about the nested-set structure. Twenty-nine participants were randomly divided into two groups, one Probability condition and one Informed probability condition, where participants in the latter condition were provided with the hint. The second aim was to investigate whether the Informed probability condition was performed more slowly, potentially due to the time-cost of more elaborated judgments. The results show that a subtle hint about the nested-set structure was able to remedy the conjunction fallacy in a forced-choice probability judgment task but not statistically reliably in a probability estimation task. No response-time differences were observed between the conditions. The results support the nested-sets hypothesis and imply that even a subtle reasoning hint clarifying the relation between categories and subcategories might remedy one of the most robust probability judgment fallacies.

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