The first trial in this instance involves a hand movement to the green diamond, which can be identified as the target because it is the object with a unique color. The next trial likewise involves the green diamond because it is again unique and therefore a target, but this time it is the eyes that have to fixate on it. The color and location of the target varied randomly from trial-to-trial.
The analysis focused on the time taken to initiate the appropriate movement of the eyes or hand. The question of interest was whether an attentional benefit resulting from repetition of the same target color—as in the above figure—would persist when effectors were switched.
It has long been known that repetition of the same target across trials yields a performance benefit in a variety of tasks. However, conventionally these benefits have been observed when all other task parameters remained the same from trial to trial.
Moher and Song found that some of the conventional target-repetition benefit was preserved even when effectors switched between trials: Regardless of whether eye movements were followed by hand movements or vice versa, responding was quicker when the target was repeated. That is, responding in the trials shown in the above figure would have been quicker than if the target on the second trial had been a single red diamond among two green ones.
This result suggests that the representations of target features in memory are stored (largely) independently from their associated actions. It also suggests that a benefit is observed from repeated access to those representations. However, the data from the first experiment by Moher and Song are equally compatible with the idea that rather than the target’s representation being facilitated
, the distractors’ representations are inhibited
This possibility was examined in a second experiment, which differed from the first one only in that on 25% of trials, no target was present. On those trials, all diamonds were either red or green, and participants had to withhold a response—that is, their hand had to stay on the table in front of them or their eyes had to stay fixated on the same spot on the screen.
The results again showed a transfer effect across effectors. When a no-target trial was followed by a trial on which the target was of a different
color, then responding was facilitated—in other words, showing 3 green diamonds followed by a display with two green and one red diamond facilitated detection of the red target. This finding is consistent with the idea that the inhibition of responding on the first trial carries over to the next trial, and because the inhibited objects now serve as distractors, this facilitates target detection.
This finding is known as a “distractor previewing effect” and replicates previous results in the literature.
Moher and Song additionally showed that responses were slower when the effector was repeated on those trial sequences than when it changed, independent of any color repetition effects. In other words, if you must inhibit moving your eyes because no targets are present, then that inhibition carries over to the next trial and you are slower to look at the target than if you had to suppress movement of your hand on the first trial.
Because the results are complex, let’s consider the figure below which shows the entire pattern of results for the second experiment conducted by Moher and Song:
The panel on the left (A) shows the results as a function of target color between two trials. This replicates the finding of the first experiment, namely that the target-repetition benefit (difference between light and dark blue bars within each pair) is not eliminated by the effector switch. The panel on the right (B) shows the benefit that is observed, again regardless of whether or not effectors switch, when a target-free display previews the color of distractors on the next trial, compared to when it previews the target color. In those cases, when no response is required, it is repetition of the distractors that is beneficial rather than repetition of the target.
In summary, across the two experiments, Moher and Song found that two well-known attentional effects in visual search—the target repetition and distractor-previewing effects—transfer between different effectors. Our attention-action system seems to be integrated across different effectors: what you focus on in your rear view mirror may affect what your hands do with the steering wheel a short time later.
Reference for the article discussed in this post:
Moher, J., & Song, J.-H. (2016). Target selection biases from recent experience transfer across effectors. Attention, Perception, and Psychophysics.