Attention & Change Blindness

What is attention? • How is the word used? • Examples: – something bright caught my attention – I didn’t see you, I was paying attention to the game – I struggled to pay attention to the lecture – I don’t remember even cleaning the table, I must not have been paying attention

• Attention refers to many different kinds of mechanisms

Attention and limits on information • We need attention to limit the amount of information that is processed • Why are there limits on the amount of information we can process?

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Attention and limits on information • Human information processing is massively parallel, up to a point Æ Serial bottleneck – limited sensory systems – limited effector systems • movements must be planned sequentially • words can only be spoken sequentially • After bottleneck, it is the allocation of our attention that determines what is analyzed • Often, we are unable to process information that is unattended Æ inattentional blindness

Magic trick to Demonstrate Inattentional Blindness • Please choose one of the six cards below.

Focus on that card you have chosen.

Magic trick (2) • I’ve shuffled the cards and removed the one which I think was your card.

Can you still remember your card?

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Magic trick (3) • Here are the remaining five cards, is your card there?

Did I guess right? Or is it an illusion?

Magic trick – The Explanation •• You just experienced Inattentional Blindness

• None of the original six cards was displayed!

Inattentional Blindness • Attention involves selective processing of visual information • Sometimes, we seem unaware of the selectivity: inattentional blindness • Lots of demos: – http://viscog.beckman.uiuc.edu/djs_lab/demos.html – http://dualtask.org/Change_Blindness_Demo/ChangeBlindness.html

Airplane demo Dinner demo

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Some of these demos are from: Simons & Levin, 1997, TINS, 1, 261-267

Inattentional Blindness • Why is it hard to notice the change (initially)? • When motion detection is disrupted, it is very difficult to observe changes to unattended image locations • Brain makes reasonable assumption that things do not change unexpectedly (in the absence of motion cues).

DVD Demo of basketball players • Task: count the number of times the white team passes the ball to each other • Important to pay close attention to task

(Simons & Chabris, Perception, 1999, 28, 1059 – 1074)

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Other demo’s Dan Simons (University of Illinois): http://viscog.beckman.uiuc.edu/change/demolinks.shtml

see also letter task: http://www.dualtask.org/

Inattentional Blindness Results demonstrate: •

Remarkable gaps in our perception

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Human’s interpretation of the visual field is much sparser than the subjective experience of “seeing” suggests

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Perception of objects requires considerable effort / resources – Attention is needed to see the change

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If attention is elsewhere (even temporarily), changes can be missed Æ implication for drivers?

The role of similarity • http://viscog.beckman.uiuc.edu/grafs/demos/28.html

Percent of participants detecting unexpected objects as a function of similarity between their luminance or brightness and that of target objects. From Most et al. (2001)

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Role of prior attention to the object

Percent correct change detection as a function of form of change (type vs. token) and time of fixation (before vs. after change); also false alarm rate when there was no change. From: Hollingworth and Henderson (2002).

Selective Attention

Focused Auditory Attention • Colin Cherry – The cocktail party effect – Cherry (1953) found that this ability involves using physical differences to maintain attention to a chosen auditory message • Moray (1959) – Unattended auditory information receives practically no processing

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Dichotic listening/ Shadowing tasks

Dichotic listening demo Focus your attention on (or shadow) the left ear, and try to remember only the details in the left ear. Quiz: 1. John ate breakfast with his father.

True False

2. A man shook his head and frowned.

True False

3. Birds were singing when John awoke. True False 4. Miles Davis was singing when John awoke. True False You probably recall the facts from the left ear's dialog much better than those of the right ear; you may not remember any of the right ear's dialog!

What gets through? What happens to unattended message? Æ Not much, we seem to remember mostly low-level information (human voice or not, changes in gender, not a change in language) (Colin Cherry) Æ Subjects names get through (30% of the time) Æ The same word can be repeated without being noticed (Moray, 1959)

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Broadbent’s Filter Theory • Sensory information is processed until a bottleneck is reached • One of the inputs is then allowed through a filter on the basis of its physical characteristics, with the other input remaining in the buffer for later processing • Early selection theory (select message by ear)

Some semantic processing though in unattended ear … • People notice their own name at parties • Treisman experiment:

Æ Problem for early selection theories

Treisman’s Attenuation theory • Messages are attenuated but not filtered on the basis of physical characteristics • Semantic criteria can apply to all messages, attenuated or not • Semantic criteria are harder to apply to attenuated messages, but still possible

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Deutsch & Deutsch Late Selection theory • Capacity limitations are in response system, not the perceptual system • All information is processed completely unattenuated

Critical Experiment (Treisman & Geffen, 1967)

• Asked to shadow one ear and tap a button when a certain word is heard in either ear, people do much worse at word detection in unshadowed ear. Æ against late selection theory

Selective Visual Attention

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Location-based Attention • Posner (1980) – Attentional spotlight: a theory which holds that we can move our attention around to focus on various parts of our visual field – The spotlight can span varying degrees of visual angle • Erikson & St. James (1986): zoom-lens model

The Cue Validity Task • Posner presented either a central cue or a peripheral cue before a target appeared. • Cues valid on 80% of the trials, invalid on 20% of the trials or vice-versa

The Cue Validity Task • When cues were valid, response times were faster than when cues were invalid.

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The Zoom Lens analogy • Spotlight has fixed size • Zoom lens is flexible in size • Experimental subjects can control whether they focus on a specific target (the middle letter of a five letter word) or spread their attention (across all the letters) (La Berge, 1983)

Evidence in Favour of the Zoom-lens Model

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Mean reaction time to the probe as a function of probe position. The probe was presented at the time that a letter string would have been presented. Data from LaBerge (1983).

Experiments Demonstrating Split Attention • Awh and Pashler (2000). • (a) Shaded areas indicate the cued locations and the near and far locations are not cued; (b) probability of target detection at valid (left or right) and invalid (near or far) locations.

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