Experimental Psychology PSY 433

1. Experimental PsychologyPSY 433 Chapter 8 Attention and Reaction Time

2. Where’s Waldo? • http://www.youtube.com/watch?v=EvWh6PMi9Ek&feature=player_embedded#

3. Two Aspects of Attention • Divided attention – what happens when we try to engage in two cognitive processes at once • Selective attention – how we switch mental resources from one cognitive task to another.

4. Visible Bottleneck Task • http://opl.apa.org/contributions/Pashler/prp.html • This task illustrates how difficult it is to pay attention to two things at the same time. • Both tasks require a choice of response and the same cognitive resource cannot be devoted to both tasks at the same time. • The competition goes away when one task does not involve a choice (e.g., press any button when you hear a tone).

5. Donders A, B & C Revisited • A is simple RT – see a stimulus and press a key • B is stimulus choice RT – see one of two stimuli and decide whether to press a key or not • C is stimulus and response choice RT – see one of two stimuli and decide which of two keys to press • B-C gives response selection time • C-A gives ID time.

6. Donders Tasks • S1  R1 Donders A • S1  R1 Donders BS2  R2 • S1  R1 Donders CS2

7. Donders A -- Simple A Reaction Time C Reaction Time C Minus A Baseline Identification Time Selection Time

8. Donders B -- Choice B Reaction Time C Reaction Time B Minus C

9. Testing for Modularity • Donders A, B & C implies that the parts of the task are modules. • How can component modules be identified? • When one component module can be changed without changing the others, it is independent. • If Donders was correct then the three parts should be separately modifiable. • Pure insertion – addition of a module without affecting the duration of the other modules.

10. Response Force • Donders pure insertion could not be tested so an additional variable was added – response force. • Response force – the amount of pressure exerted on a response key. • Force increases with stimulus intensity. • For Ulrich et al. (1999), response force was the same for a Donders A and B comparison, even though RTs were different.

11. RT and Integrated Force (Fig 8.3) This result is consistent with pure insertion.

12. B and C Reactions (Fig 8.4) The B and C RT’s should differ but they do not.

13. A and C Reactions (Fig 8.5) Now RT’s differ as they should but force is not consistent with pure insertion.

14. Confounding Stimulus Intensity • Confound – when one or more independent variable is simultaneously varied so we can’t tell which is responsible for an effect. • In Ulrich et al.’s experiment (green LED to left or right), two things were varied: • Mapping of stimulus to response (one hand vs two) • Apparent brightness (focusing on a single light instead of both lights) • Replaced by letters X and S not lights.

15. The Same Experiment using Letters not LED Lights (Fig 8.6) Now RT differs as it should and Force supports pure insertion.

16. Results using Letters • When X vs S is used, the confounds of stimulus intensity and handedness are eliminated (controlled) and the results support pure insertion. • Part of the problem is that all three Donders experiments were not presented: • Authors wished to avoid transfer effects that occur in within-subject experiments. • To avoid this, present all three Donders conditions or do the experiment between-subject.

17. Speed Accuracy Tradeoffs • RT cannot be used as the only dependent variable because subjects change accuracy to maximize speed: • Speed & accuracy are sometimes inversely related. • RT & Accuracy must be jointly considered. • Examining more than one dependent variable may be crucial to understanding the processes involved in a task.

18. Theios (1973) • Subjects had to name a digit presented visually. • Probability of the digit was varied from 0.2 to 0.8. • Reaction time was unaffected by probability of the digit, but accuracy was greatly affected. • Highest error rate with lowest probability. • To increase accuracy (keep error rate constant), RTs would have to increase.

19. RT and Error Rate as a Function of Stimulus Probability RT stays constant but as stimulus probability increases, errors decrease.

20. Dual Task Processing

21. Speed-Accuracy Tradeoff SOA (S1-S2 Interval in ms)

22. A Central Bottleneck • We can only process one thing at a time within a single modality (vision, hearing). • Central cognition may be the most important bottleneck – the central bottleneck. • Whether two tasks can be done at once depends on whether they compete for the same resources. • Schumacher dual-task experiment.

23. Stimulus Onset Asynchrony (SOA) • Pashler presented a modified Donders B task in which S1 and S2 were not presented simultaneously. • The interval between them is called stimulus onset asynchrony (SOA) • The shorter the SOA, the greater the effect on RT and errors. • The period where one task interferes with the other is called psychological refractory period.

24. Dual Task Processing

25. Pashler’s Paradigm • Task 1 – hear a tone and press a key with the left hand. • Task 2 – vocally call out the name of the highest digit in a display of eight digits. • When subjects are not required to respond quickly to Task 2, accuracy is not affected. • It only occurs with a requirement to make a speedy response.

26. Capacity Sharing Explanation Response selection S1 Response selection S2 The resource is shared during the time when the tasks overlap.

27. Explanations • Central bottleneck models – some common internal processing stage is required by both tasks, creating a bottleneck for resources. • Central capacity sharing models – a resource called capacity must be split across the two tasks, reducing the capacity available to either task and reducing efficiency. • Both models predict the same observed results – the author prefers capacity models.

28. Stress and Cognitive Control • Two possible effects of stress on cognition: • Stress requires attention (capacity) thus decreasing performance. • People adapt to stress by finding more efficient ways of doing tasks increasing performance (strategies change). • Steinhauser’s experiment: • Long/short interval cues to respond to digit or letter – 6M • Is letter a consonant/vowel, is digit odd/even?

29. Results • For the low stress condition there was an interaction between stimulus interval and task repetition (same task next or different next). • No interaction in the high stress condition. • Under low stress there was a relatively higher cost to changing tasks quickly. • Under high stress the cost was the same. • This is consistent with the idea that under stress cognitive strategies change.

30. Change Blindness Demo • http://viscog.beckman.illinois.edu/flashmovie/23.php