Monday, May 3, 2010

Implicit sequence learning in a search task

The purpose of this study was to see how the selection process is affected by task demands; that everyday skills rely on implicit sequence learning where learning happens unintentionally and the effects are beyond the learners’ ability to report on exactly what they learned. The researchers’ intent was to investigate whether learning about a sequence of stimuli appearing as part of a complex scene can be different from responding to a single target.


Participants were presented with eight digits distributed pseudo-randomly over 16 possible locations arranged on an invisible 4X4 matrix. The targets followed a sequence that learners could exploit to improve performance. The researchers compared sequence learning under this seemingly demanding task with two different control conditions in which the perceptual load was lower. In a first control group, perceptual load was decreased by removing the distracters, but the target appeared at the same variable locations, in order to analyze whether the spatial uncertainty could produce any effect independent from perceptual load.

In the second control group, the researchers removed both factors by presenting the targets alone at the center of the screen. Because the search conditions were expected to hinder the achievement of explicit learning, they arranged a known sequence rather than a probabilistic procedure.


A total of 90 students participated in the experiment and a total of 30 participants were assigned to each condition: central, variable location, and search.

The stimuli consisted of a set of colored digits over a grey background. Target stimuli were even numbers presented in random colors. In the central condition, the target was presented alone at the center of the screen. In the search condition, the target appeared on each trial at one of the 16 locations defined by an invisible 4X4matrix. The location of the target was decided pseudo-randomly on each trial, with the only constraint that all 16 possible locations should be sampled before any of them was repeated. The distracters were seven instances of the same odd number, randomly chosen for each trial from the numbers 1, 3, 5, 7. The seven distracters plus the target stimulus were colored and located pseudo-randomly, so that two of them were drawn in each possible color and two items were located at each one of the matrix quadrants. At the end of the experimental blocks, participants performed a cued generation task, designed to measure their ability to predict the more likely successor.


The study showed that implicit sequence learning does not depend on the resources demanded by the selection task. The results indicate that implicit sequence learning is resistant to selection demands, and that presenting the targets at variable locations can be useful to control for the acquisition of explicit learning.

The full results of the experiment can be accessed through Academic Search Complete: Implicit sequence learning in a search task by Luis Jime´nez and Gustavo A. Va´zquez. The Quarterly Journal of Experimental Psychology, 2008.

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