The Effects of Feature-Based Attention on the Discrimination of Letters and Numbers

Abstract

Feature-based attention refers to the phenomenon that attending to a feature value (e.g., a specific shade of red) enhances the detection of similar feature values (e.g., the same shade of red or other shades of red similar to the attended shade) relative to different feature values (e.g., green) that belong to a different object, and that this facilitation effect can be found across the visual field. In previous studies, the participants’ task was primarily the detection or discrimination of simple features such as orientation, colour or motion. The experiments reported in this thesis investigated whether feature-based attention could also influence the speed and/or accuracy of discriminating alphanumeric stimuli such as letters and numbers. In three experiments, participants saw displays that consisted of a series of stimulus patterns at a central location followed by the appearance of an alphanumeric stimulus at one of two peripheral locations. Experiment 1 tested whether paying attention to a specific orientation in a central stimulus would affect the speed and/or accuracy of identifying a peripheral letter whose principal axis was either the same as or different from the attended orientation of the central stimulus. Experiment 2 changed the peripheral stimulus from a letter to a number. In Experiment 3, a peripheral stimulus occurred randomly on 50% of the trials instead of on 100% of the trials. The results showed that attending to a specific orientation of a central stimulus could affect the processing efficiency of both letters and numbers at a peripheral location when the alphanumeric stimulus occurred on every trial (Experiments 1 and 2), but not when it appeared on 50% of the trials. These results suggest that feature-based attention could influence the identification of alphanumeric stimuli. However, the effect may be quite short-lived.