Dual-Task Interference 1
We are often confronted with having to make different responses to different stimuli. This becomes more difficult as the time between the presentation of multiple stimuli decreases. Cognitive psychologists study this by varying stimulus onset asynchrony (SOA), the difference between onset times between stimuli. The SOA manipulation forms the basis of this lab activity, which explores the role of attention in dual-task interference.
Perceptual Refractory Period Paradigm
There are two discovery labs related to dual-task interference. This one introduces the perceptual refractory period and should be completed first. This lab activity consists of 10 practice trials and 60 experimental trials. On each trial after you see a fixation +, you will be presented with two stimuli. One will be a letter and one will be a tone. If the letter is an “O,” press the “S” key. If the letter is an “X,” press the “D” key. If the tone is high pitched, press the “K” key. If the tone is low pitched, press the “L” key. Accuracy is as important as speed in this activity so respond to both stimuli quickly and carefully to minimize incorrect responses. You will receive feedback on each trial.
Response Times as a Function of SOA
The results show response times to the tone as a function of how soon after the letter appeared the tone was presented (i.e., the SOA). Only trials where both responses were correct are shown. There are two key findings. The first key finding is that response times to the letter are not affected by how close in time the tone followed the presentation of the letter. This is because the letter task is always begun before the tone presentation, so the same amount of attention is available at all SOAs. The second key finding is that responses to the tone get faster as the SOA increases. This is because at short SOAs, attention is not available to complete the tone task; attention is being allocated to complete the letter task. However, at longer SOAs, when the letter response has been made before the tone is presented, response times to the tone are much faster because the participant can give full attention to the tone task as soon as it is presented.
The Refractory Period
When the SOA is too short, longer response times reflect interference and the existence of a perceptual refractory period (PRP) where participants cannot give their full attention to the tone task because attention is still allocated to the letter task. Effects like these have been replicated over and over by other experimenters. When experimenters try paradigms that do not involve making a choice about the stimulus, they find little evidence for dual-task interference. This suggests that when dual-task interference is not observed between two tasks, one or both tasks require little or no attention to complete.
Practical Implications
Results from PRP experiments have practical implications. Take driving for example. PRP experiments show that even simple tasks can reduce the ability to make quick decisions. As there is always a chance of something unexpected occurring while driving a car, distracting items such as cell phones should not be used at all by drivers. Pressing the keypad on your phone in response to a text is one task. Pressing the brake in response to an unexpected road event is another task. If you allocate attention to the former and need to make a quick stop because something happens on the road, you will have less attention to devote to braking and you will take longer to do it.