Presentation on theme: "4 – Divided Attention divided attention trying to do two things at the same time Some dual tasks cause no interference. Example Walk and chew gum Some."— Presentation transcript:
4 – Divided Attention divided attention trying to do two things at the same time Some dual tasks cause no interference. Example Walk and chew gum Some dual tasks cause interference. Example Drive and talk on cell phone. Question What kinds of tasks can be done concurrently without interference?
DemoTask A = Rotate right arm clockwise. Task B = Rotate left arm counterclockwise A & B no interference DemoTask A = Rotate right arm clockwise. Task B = Rotate right leg counterclockwise A & B interference Typical Divided Attention Experiment 3 conditions: A only B only dual-task (A and B at the same time) dual task interference occurs if Performance on A is better during A-only condition than during dual-task. orPerformance on B is better during B-only condition than in dual-task.
Laws prohibiting cell phone use while driving (as of 2013) For experienced drivers, hands-free phone banned in 0 states. Handheld phones banned in 10 states (but not Florida). Texting while driving is banned in 41 states, including Florida. In Florida, texting is “secondary offense” (Source - Insurance Institute for Highway Safety)
Driver Distraction Common belief: Driving is unaffected by driver’s use of hands-free phone Typical explanation. The two tasks are very dissimilar. driving car visual, spatial, manual talking on hands-free phone oral, verbal, auditory Laws conform to this belief. Use of handheld phones prohibited in many states. Use of hands-free phones allowed in every state (as of 2011). Does this make sense? Or do hands-free phones also cause interference?
Driver Distraction experiments Task Ss drive in simulators Ss must avoid cars, pedestrians. Typical Measures Braking time Number of collisions Common Conditions driving while talking on handheld phone driving while talking on hands-free phone driving while talking to passenger driving while reading text driving while composing text driving intoxicated
Experiment: Effect of hands-free phone Ss drove in simulator. During dense traffic, car in front stopped unexpectedly. Sample resultBrake Time (ms) no distraction 933 talking on hands-free phone1112 Conclusion Interference is attentional – not just manual. (Strayer et al., 2003)
Experiment: Hands-free phone vs. Intoxication Ss drove in simulator. Car in front suddenly stopped. One result: Brake time (ms) intoxicated (BAC 0.08%)779 hands-free phone849 (Strayer et al., 2011)
Experiment: Is hands-free phone worse than talking to passenger? “… Passengers tend to adjust their conversation based on driving difficulty; often helping the driver to navigate and identify hazards on the roadway and pausing the conversations during difficult sections of the drive. By contrast, this real-time adjustment based upon traffic demands is not possible with cell phone conversations.” Strayer and Drews (2006, p. 130) Experiment S drove in simulator; was asked to exit the highway at rest stop “about 8 miles away” S listened to friend tell story Result: Drivers who Missed the Exit driving alone 4% passenger conversation12% hands-free cell phone conversation50% (Drews et al., 2008)
Other findings from driver distraction studies: Most Ss overestimate their ability to drive while using a hands-free phone. Hands-free phone as bad as handheld phone Four 1-minute videos (bottom of webpage) Strayer and his colleagues (2001, 2003, 2006, 2009)
Bottleneck Experiments Driving and talking are hard tasks. Can interference occur if tasks are dissimilar and easy? Procedure Task 1 S 1 Hear high or low tone R 1 say “high” or “low” Task 2 S 2 See “A” or “B” R 2 press left or right key RT 1 RT 2
Ss practiced task 1 alone, task 2 alone, and dual task. Practice trial data were excluded from final analysis. Results: RT 2 Task 2 alone~ 500 ms Task 2 in dual task~ 700 ms Conclusion Even two easy, dissimilar tasks can yield massive dual-task interference. (Pashler, 1984; Welford, 1941)
Why does Task 2 take so long? That is, in which stage does interference arise? Perception Response Selection Response Production Perceive high toneSince tone is high, say “high”Say “high” Perceive “A” Since letter is A, press left key Press left key. Hypothesis: The mind can perform only one “response selection” at a time.
Two findings showing bottleneck during Response Selection Manipulation Effect on RT 1 Effect on RT Task 2 Perception made harder nonenone (e.g., “A” appeared blurry) Task 2 Response-Selection made harder noneincreased (e.g., if “A” then press B key) (Pashler, 1984) RT 2 lag wait RT 1
Bottleneck Practice Questions Predict the effect of each manipulation on RT 1 and RT 2 Manipulation RT 1 RT 2 Harder P 1 increaseincrease Harder P 2 none none Harder RS 1 increase increase Harder RS 2 none increase Harder RP 1 increase none Harder RP 2 none increase RT 2 lag wait RT 1
Another Prediction: Increasing lag by 1 ms should shorten RT 2 by 1 ms (up to a point) RT 2 = 550 lag wait RT 2 = 600 lag wait
Another Bottleneck Experiment Same Basic Procedure Task 1 S 1 Hear high or low tone R 1 say “high” or “low” Task 2 S 2 See “A” or “B” R 2 press left or right key Lag between S 1 and S 2 varied from 50 to 900 ms (continued) RT 1 RT 2
Prediction of bottleneck theory Actual data (Pashler, 1984) RT 2 Lag between S 1 and S 2 RT 2 Lag between S 1 and S 2 Slope = -1 RT 2 Lag between S 1 and S 2 RT 2 Lag between S 1 and S 2
What dual-tasks can be done without interference? Distinction choice-RT task Examples Tasks used in bottleneck studies simple-RT task Examples hit key as soon as light appears catch ruler dropped between your fingers Two choice tasks interference Two simple tasks no interference One simple, one choice no interference PerceptionResponse SelectionResponse ProductionPerceptionResponse Production
Summary of Bottleneck Studies Many easy tasks require “response selection.” If people try to do two such tasks concurrently, one task must wait (bottleneck). The bottleneck occurs if both tasks need “response selection”
Task Switching If we cannot do two things at once, can we at least switch back and forth? Yes, but switch is costly task 1 alone task 2 alone Switch without cost Switch with cost Data show that switch cost is high.
Experiment Ss shown two category names (e.g., Insect, Vegetable) Ss immediately say 4 examples of each category as quickly as possible Ss told in advance that responses should be: blockedAAAABBBB antgnatmothflybeancornpeayam or alternatingABABABAB antbeangnatcornmothpeaflyyam Result Alternating is almost twice as slow! Conclusion Switching is costly.
Mental Rotation demo Indicate whether F is mirror-reversed or normal
Mental Rotation Letter Rotation Experiment Indicate whether letter can be rotated so that it looks normal. noyes IV = amount of rotation 135° 30°
Results Interpretation Ss “mentally rotated” object at constant rate 800 RT(ms) rotation (degrees)
Demo: For each pair, indicate whether two images depict same object. yes no
More examples yes no
3D mental rotation experiment Ss saw pairs of images depicting 3D objects. For each pair, Ss indicated whether two images depict same object or different objects. When images depicted the same object, it was rotated. within the plane or in depth (continued)
Span Task S hears 3 – 10 items (digits or words), typically at a rate of item per second Immediately afterwards, S tries to repeats items aloud in same order DV = span = number of items S can report in the correct order Digit span task used on many IQ tests. (e.g., Baddeley, 2003; Cowan, 2005)
How do people perform the span task? rehearsal loop Mental mechanism that is used to rehearse verbal info (silently or aloud) Examples Rehearsing a phone number until you have a chance to jot it down Rehearsing someone’s name so you’ll remember it later. Mental arithmetic 23 x 15 = (20 x 15) + (3 x 15) = = 345
Does span increase if items rhyme? who blue view do coup you true book love trap wait bird head wall rake bake make lake take cake fake rope dark hand moon soft fear edge
Word Span Experiment Each list included 7 words. Two kinds of lists: rhyme and non-rhyme Resultsrhyme span
How many items can you hold in your rehearsal loop? 7 ± 2 ? Demo 6 words on each list association opportunity representative organization considerable immediately sum hate wit bond yield twice
Another Word Span Experiment Ss perform word span task Each list included 6 words. Two kinds of lists: short words (1 syllable each) and long words (5 syllables each) Results long-word span
If magic number is wrong, why does digit span equal about 7? Observation IQ tests reveal that English kids had greater digit span than Welsh kids Experiment Welsh-English bilinguals tested in both languages Results: English digit span > Welsh digit span Why? English digit words are shorter than Welsh digit words (Ellis & Hennelly, 1980)
Arabic Digits 1. wahed 2. ithnan 3. thalatha 4. arba 5. khamse 6. sitta 7. seba 8. thamanya 9. tesa 10. ashara Cantonese Digits 1. yat 2. yih 3. saam 4. sei 5. ngh 6. luhk 7. chat 8. baat 9. gau 10. sahp Prediction If digit span = 2 sec, then digit span should vary by language so that digit span = number of digits that can be said in 2 s
Cross-Language Digit Span Experiment E measured how fast Ss could read digits in their native language E measured Ss’ digit span in their native language Results Languagesyllables per digit words read in 2 sdigit span Arabic Spanish English Thus, digit span = number of digits that can be said in about 2 seconds. Conclusion Magic number 7 is merely an artifact of the English language. (Naveh-Benjamin & Ayres, 1986; see also Stigler, Lee, & Stevenson, 1986)
Sign Language In ASL, some words take longer to sign Long signs include PIANO, BICYCLE, CROSS Short signs include TYPEWRITER, MILK, CHURCH Word span is shorter if signs are long. (Wilson & Emmorey, 1998)
Sometimes, we need to “work with” or “hold information” that is visual Questions How many windows are on the front of your house? If you’re traveling south, and you must turn east, do you turn left or right?
Demo chunking increases span by reducing number of items
visuospatial scratchpad Used for temporary storage and manipulation of spatial and visual information Examples Visualizing the campus layout in order to give someone directions. If you’re traveling south, and you must turn east, do you turn left or right?
Are visual-spatial scratchpad and rehearsal loop truly different mechanisms? Experiment Dual-task Results Both verbal hard Both visual hard One of each easier (Baddeley & Hitch, 1974; Brooks Cocchini et al., 2002; Fougnie & Marois, 2006)
Demo Verbal Task As the woman chased her poodle, her poodle chased a cat Spatial Task Spatial Responsepoint to “yes” or “no” Verbal Responsesay “yes” or “no” (Brooks, 1968)
What is meant by analog? Example On hard drive, similar images have dissimilar representations (digital) 12:59:59 and 1:00:00 look similar on analog clock (but not on digital clock)
Implications of mental rotation studies… 1. Mental imagery can be studied objectively and quantitatively (without relying on introspection). 2. Linear RT growth suggests that images are mentally rotated.
demo How many left turns as you drive from ● to ▲ ? … right turns?
Subtraction method has untenable assumptions. 1. Stages are non-overlapping. For example, RP might begin before RS complete. 2. Stage durations are independent. Duration of RP might depend on duration of RS. Still, in some cases, subtraction method has utility.
Demo How fast does sensory info (e.g., ankle twist) move from ankle to brain? Compare ankle and shoulder: E taps S’s ankle or shoulder; S raises finger Since d = r t d r = t 1.5 m = = 150 m/s 0.01 s
Fact from textbook Impulse along myelinated axon can move as fast as 120 m/s = 260 mph
Demo – semantic similarity Same task as before. cat dog pig horse goat sheep cow hen sky nail nurse box light noise shirt grass
Some details from study by Naveh-Benjamin and Ayres (1986) SyllablesDigitReading Aloud rate Language Per DigitSpan (in digits / 2 sec) English Spanish Arabic
Mental Rotation Experiment Ss first became familiar with several irregular polygons. On each trial, Ss saw one of the polygons or its mirror image. TaskIt is the same or mirror-reversed? (continued)
Alternative version: stimuli = irregular polygons ( rotation
What about 3-D mental rotation? (
Visual tasks and verbal tasks are controlled by different mechanisms. Evidence dual-task studies Both verbal very hard Both visual very hard One of each easier KF (motorcycle accident) visual storage okay, verbal storage imparied (Baddeley & Hitch, 1974; Brooks Cocchini et al., 2002; Fougnie & Marois, 2006)
latent bottleneck (Lien et al., 2006) RT S 1 - S 2 Lag
Why exactly does this dual-task interference occur? Traditional Explanation Resources are limited, so progress on at least one task is slowed. Task 1 alone| | Task 2 alone| | 500 Dual-Task Task 1| | Task 2 | | 700 (continued)
Bottleneck Theory During certain stage in completion of Task 2, progress completely stops. Task 1 alone| | Task 2 alone| | 500 Dual-Task Task 1| | Task 2 | wait | 700 In other words, at some point, Task 2 must wait for Task 1.
Experiment Ss saw between “study letters” at rate of one per s Then Ss saw target letter. Ss hit yes or no key, depending on whether target was a study letter. For target-absent trials, task included : Perceive Target Mentally scan study letters, one at a time Select response (“no”) Produce response Results: Each additional study letter increased RT by 38 ms Conclusion : Ss “mentally scanned” letters at rate of one per 38 ms (For complicated reasons, this interpretation is no longer popular.) (Sternberg, 1966)
Bottleneck finding conflicts with traditional view of dual-task interference: limited resource theory tasks can be done concurrently and without interference if demand < supply. (e.g., Kahneman, 1973; Pashler, 1984; Welford, 1941)
Everyone knows what attention is. (James, 1890) A formal definition of the term “attention” is not presently available… (Pashler & Johnston, 1998)
Demo Even two easy tasks can cause dual-task interference Easy: Pat head and stomach Harder: Pat head, rub stomach Easy: R hand CW, R foot CW. Harder: R hand CW, R foot CCW.
Sample Experiment Ss shadowed 10 words presented to one ear. At same time, S tried to remember 10 other items simultaneously. 1) seen as pictures 2) seen as words 3) heard as words (in other ear) Then Ss tried to recall the 10 non-shadowed items. Results (3) was hardest; (1) was easiest. Conclusion Task similarity increases dual task interference. (Allport, Antonis, & Reynolds, 1972)
Statistic In 2009, cell phone use was a factor in 995 driving fatalities in US (NHTSA).
3 possible locations of bottleneck Perception Bottleneck | P | RS | -- RP 1 -- | lag |--wait--| P | RS | -- RP 2 -- | Response-Selection Bottleneck | P | RS | -- RP 1 -- | lag | P | wait | RS | -- RP 2 -- | Response-Production Bottleneck | P | RS | RP | lag | P | RS |-- wait--| RP |
Bottleneck Experiment 1 Ss did two choice-RT tasks described in previous study (see/press & hear/say). E varied difficulty of P 2 Hypothesis Predicted Effect on RT 2 Bottleneck during Perception increase Bottleneck in Response Selectionno change Results no change Conclusion no bottleneck during Perception (Pashler, 1984)
Bottleneck Experiment 2 Ss performed the two choice-RT tasks described in previous study. E varied difficulty of RS 2 HypothesisEffect on RT 2 Bottleneck during Response Selection increase Bottleneck during Response Production no change Results increased ConclusionBottleneck does not occur during Response Production (Pashler, 1984)
Practice Questions Assume bottleneck in Perception stage. Indicate effect on RT 1 and RT 2 Manipulation RT 1 RT 2 Slightly harder P 1 increaseincrease Slightly harder P increase Slightly harder RS 1 increase ---- Slightly harder RS increase Perception Bottleneck | P | RS | -- RP 1 -- | lag |--wait--| P | RS | -- RP 2 -- |
Assume bottleneck in Response Production stage. Indicate effect on RT 1 and RT 2 Manipulation RT 1 RT 2 Slightly harder P 1 increaseincrease Slightly harder RS 1 increaseincrease Slightly harder RS Slightly harder RP 1 increase increase Response-Production Bottleneck | P | RS | RP | lag | P | RS |-- wait--| RP |
An analogy showing why initial slope of -1 supports bottleneck Suppose two customers visit ATM and each requires exactly 1 minute ATM can handle only 1 customer at a time, so bottleneck occurs RT 2 equals the time Customer 2 is at the ATM Lag between their arrivalCustomer 2 time at ATM (including wait) 0:151:45 0:301:30 0:451:151:00 1:151:00 1:301:00 Thus, adding 15 s to lag simply adds 15 s to RT 2 unless Customer 1 has already left
A diagram showing why initial slope of -1 supports bottleneck S 1 R 1 Task 1| | S 2 R 2 Task 2|….lag….| wait | | S 2 R 2 |………lag……….|- -wait -| | Remember: RT 2 = time between S 1 and R 2 So, add 1 ms to lag shorten wait by 1 ms reduce RT 2 by 1 ms
Actual Data: (Pashler, 1984) RT 2 (ms) Lag (ms)
Optional: Results of last two studies inconsistent with P or RS bottleneck Perception Bottleneck | P | RS | -- RP 1 -- | lag |--wait--| P | RS | -- RP 2 -- | Response-Selection Bottleneck | P | RS | -- RP 1 -- | lag | P | wait | RS | -- RP 2 -- | Response-Production Bottleneck | P | RS | RP | lag | P | RS |-- wait--| RP |
Illustration of CEO Dual-task Xhear/say one passage & read/type another Dual-task Y hear/type one passage & read/say another Which dual-task creates more dual-task interference? Y Example For both tasks in X, stimulus = response Hear “iz”, say “iz” For both tasks in Y, stimulus responseHear “iz”, type “is” Thus, both tasks in Y require a more difficult “response selection” (Shaffer, 1975)
Results Data are linear. intercept = 1 s slope = 1 s / 60° Every additional 60° of stimulus rotation increased RT by 1 s Interpretation Ss “mentally rotated” mental image at rate of 60° per sec ClaimMental rotation data are observable measure of “mental imagery” (Shepard & Meltzer, 1971) 4 RT(s) rotation (degrees)
Demo rectangle trapezoidparallelogram
Demo pentagrampentagram within pentagonhexagram
Mental Imagery Many people believe that they can form mental image of familiar object. Experiment Ss were asked question about simple shape Example Does this include a rectangle?” Two ConditionsPerformance Answer question while looking at shape. Perfect See shape. Form mental image. Answer question. Poor Conclusion People overestimate their ability to form mental image (Reisberg, 1993)
However, “mental imagery” does appear to have a visual component. Experiment Ss told to “think about” a cat OR “form mental image” of a cat While they did that, Ss were asked: Does the cat have a head? or Does the cat have claws? ResultsQuestion Answered More Quickly Thinkers claws Imagers head (Kosslyn, 1976)