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Eye movements correlated with the feature-positive effect

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Feature-positive (FP) and feature-negative (FN) stimulus arrangements involve common elements (A) and a distinctive element (B). These are used in simple discriminative tasks (go/no-go), in which there is AB+ reinforcement and AA- extinction for FP group, whereas there is AA+ reinforcement and AB- extinction for FN group. The feature-positive effect is shown when the FP group is faster than the FN group in developing discriminations. The feature-positive effect literature has documented auto-shaped observing responses under the control of the distinctive stimulus. However, such responses have been inferred from artificial motor responses to external devices. Four studies were conducted aimed at replicating the feature-positive effect with adult humans, measuring it by means of the discriminative index, the latency and the proportion of natural observation of stimuli arrangements. First, a preliminary study evaluated and confirmed that a monocular eye-tracker was sufficient to detect subtle changes in the proportion of observation at the discriminative stimuli, as a consequence of the (conditioned) reinforcement effect intrinsic to them, which was, hypothetically, an essential component of the feature positive effect. Remaining studies replicated the feature positive effect, Study 2 and 3 with group designs and Study 4 with a single-subject design. The stimuli of the FP and FN arrangements were observed in a regularly and predictably different manner, with more observation of the distinctive stimulus during AB+ arrangements in Study 2 and Study 3. However, more observation of the distinctive stimuli was not necessary in Study 4 with which a stronger feature positive effect occurred. Key-words: feature positive effect, observing responses, eye-tracking, human adults.
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