1. Limits on Ability to Perform Different Tasks Simultaneously Two basic issues: 1. Task-Specific Resources 2. Task-Independent Resources

2. Verbal Judgments Verbal Responding Spatial Judgments Spatial Responding OK! Interferes

3. Present Stimulus Subject Responds Reaction Time Reaction Time Tasks Simple Reaction Time (~200 msec) Choice Reaction Time (300 msec ++) Task-General Resources

4. stimulus 123 button1button2button3 stimulus ABC button1button2button3 Task 1 Task 2

5. Perceptual Processing Decision/ Response Selection Response Production Present Stimulus Subject Responds Reaction Time Processing Stages in Choice RT Tasks Question: Can people do two tasks this simple at one time?

6. Psychological Refractory Period experiment (Telford, 1931) Present Stimulus 1 Response 1 Reaction Time 1 Present Stimulus 2 Response 2 Reaction Time 2 Delay

7. Reaction Time 1 Reaction Time 2 Delay from S1 to S2 Reaction Time There is dual-task interference! (Same results for almost all task pairs, whether similar or not.) PRP effect “Psychological Refractory Period”

8. Stimulus 2 Response 2 Reaction Time 2 Delay Response 1 Reaction Time 1 Stimulus 1 Total Time for both task Total Time < (Task1 + Task2)

9. Perceptual Processing Response Selection Response Prod. All task elements can occur in parallel except for response selection Response Selection Bottleneck Model (e.g. Pashler, 1991) Perceptual Processing Response Selection Response Prod. …”slack”... Delay Response selection for Task 2 has to wait until response selection for task 1 is completed

10. stimulus ABC button1button2button3 stimulus ABC button1button2button3 Task 2 easy mapping Task 2 hard mapping

11. Perc. Resp. Sel.Resp. Resp. Sel.Resp.Perc.Resp. Sel.Resp. Resp. Sel.Resp. Easy Response Selection Hard Response Selection Perc. Delay Perc. Delay

12. Delay from S1 to S2 Reaction Time 1 Reaction Time 2 Delay from S1 to S2

13. Delay Reaction Time 1 Reaction Time 2 Delay Hard task 2 response selection = Easy task 2 response selection Hard response task 2 selection Easy task 2 response selection

14. Perc.Resp. Sel.Resp. Easy Task-2 Perception Hard Task-2 Perception Resp. Sel.Resp. Perc. Resp. Sel.Resp. Perc. Resp. Sel.Resp. Delay Perc. Delay The increased perceptual difficulty gets absorbed in the slack time, with no extra-cost for the secondary task

15. Delay from S1 to S2 Reaction Time 1 Reaction Time 2 Delay from S1 to S2

16. Delay Reaction Time 1 Reaction Time 2 Delay Hard task 2 percept. = Easy task 2 percept. Hard task 2 percept. Easy task 2 percept. “Absorption into slack”

17. Perc. Resp. Sel.Resp. Perc. Resp. Sel.Resp. Perc.Resp. Sel.Resp. Perc. Resp. Sel.Resp. Easy Response Selection Hard Response Selection Delay With no response selection bottleneck…

18. Delay Reaction Time 1 Reaction Time 2 Delay Hard task 2 response selection = Easy task 2 response selection Hard response task 2 selection Easy task 2 response selection If there is absolutely no bottleneck…then there will be a constant difference between easy and hard task 2 RT across all delays…in addition, there should be no rise in RT at even the shortest delays...