MORE THAN MEETS THE EYE: STIMULUS-RESPONSE COMPATIBILITY EFFECTS IN EYE MOVEMENTS

Distinctions between set- and element-level compatibility have been made regarding stimulus-response compatibility (SRC) effects. Prior research has revealed a relationship between these two types of compatibility such that an increase in set-level effects results in an analogous increase in element-level effects. There are different ways that location information can be conveyed visually: location-words (“left” and “right”), directionalarrows (pointing left and right), and physical-locations (stimuli appearing in the left or right areas of the visual field). Set-level compatibility is higher for location-words paired with vocal “left”-“right” responses than for the other two stimulus modalities, and vice versa for pairings with left-right keypress responses, and the element-level compatibility effects differ in size accordingly.

My dissertation research focused on examining set- and element-level compatibility effects within the saccadic eye-movement system. These effects were considered within the dimensional overlap framework proposed by Kornblum, Hasbroucq, and Osman (1990), according to which the element-level mapping effects are an increasing function of set-level compatibility. All experiments were conducted using introductory psychology students.

In Experiment 1, participants responded using a left-right unimanual joystick movement or eye movement to a location-word or physical-location stimulus. In addition to an analysis of variance (ANOVA) of mean reaction time (RT) and response accuracy for the respective conditions, compatibility effects across the RT distribution were investigated by dividing trials into quantiles. Experiment 1 produced a set-level compatibility effect for the congruent mapping: Eye-movement responses (rather than joystick movements) were found to be relatively more compatible with physical-location stimuli than with location-word stimuli. In addition, the high set-level compatibility conditions exhibited a larger element-level mapping effect than the low set-level compatibility conditions. RT distribution analysis showed that both eye- and joystickmovements yielded a steadily increasing element-level mapping effect across bins, except for physical-location stimuli mapped to joystick responses, for which the function was flat.

In Experiment 2, the location-word stimuli used in Experiment 1 were replaced by directional-arrow stimuli. Eye movements (and not joystick movements) showed larger set- and element-level SRC effects when paired with physical-location stimuli than with directional-arrows. As in Experiment 1, the physical-location stimuli paired with eyemovement responses demonstrated an increase in the element-level mapping effect across the RT distribution. However, for the three other three set-level pairings, the elementlevel mapping effects were relatively constant across the RT distribution. This pattern further indicates a preferential benefit for eye movements paired with physical-location stimuli.

Experiment 3 directly compared the location-word stimuli used in Experiment 1 and the directional-arrow stimuli used in Experiment 2. The element-level mapping effect was larger for location-words than for directional-arrows, but both types of stimuli produced similar interaction patterns regarding the set-level manipulation. That is, the differences between each response modality and stimulus type produced similar patterns of element-level mapping effect differences. The location-word stimuli produced consistently large effects and served as a driving factor across the set-level comparisons. The location-words showed a large increase in element-level mapping effect across the RT distribution compared to only a small increase for the directional-arrows, which in both cases did not differ between eye- and joystick-movement responses.

Together the three experiments provide support for the hypothesis that eyemovement responses to physical-location stimuli are a unique, highly optimal set-level pairing relative to location-words or directional-arrows denoting spatially relevant location. In the context of a continuum outlining the relative position of different response and stimulus pairings, the results imply that eye-movement responses are similar in compatibility to joystick movements, except for the specific pairing with physical-location stimuli.

The results offer some support for Kornblum et al.’s (1990) account that suggests a tightly coupled relationship between set- and element-level compatibility effects. Not only do the results provide understanding about the existence of compatibility effects within the saccadic system, they allow for some considerations about how attention is allocated preferentially to certain stimuli rather than others. They also enable predictions about similar underlying mechanisms that might be involved in saccadic and manual response modalities. Taken together, it seems that the eye-movement system adheres to conventional notions about motoric behavior; however, it also has its own unique properties that make it highly tuned to exogenously guided stimuli.