Presentation on theme: "1 Cognition and Perception for PS1000 Dr. John Beech (for 8 lectures)"— Presentation transcript:
1 Cognition and Perception for PS1000 Dr. John Beech (for 8 lectures)
2 Cognition and Perception: John Beech Lecture Topics 1.Selective Attention (2) 2.Perception (2) 3.Pattern recognition (1) 4.Speech recognition (1) 5.Visual imagery (1) 6.States of consciousness (e.g. meditation, hypnosis) (1)
3 Topic 1: Selective Attention
4 Selective Attention Overview Cherry and the shadowing task – and its problems Broadbent’s bottleneck theory Treisman’s attenuation theory Deutch and Deutch’s model Visual attention Parallel processing Meta-attention
5 Selective Attention Introduction The concept of "attention" was regarded as important by psychologists and philosophers. There are at least 4 functions of attention…
6 Selective Attention Four functions of attention 1. Focussing: Attention can be taken to mean the ability to select just one aspect of information (e.g. limiting the number or items processed.) 2. Selecting: Attention can also apply to our ability to select to attend to something (e.g. rather than daydream, or selecting an action to do next.) 3. Perceptual enhancement: Increasing the gain of a stimulus (e.g equivalent to turning up the car radio to hear better) – listening more intently. 4. Sustaining attention: Persisting in concentrating on something in the face of other distractions. (We’ll look at this later under “met-attention”.)
7 Selective Attention Cherry (1953) initiated first systematic work on attention. Interested in “the cocktail party phenomenon” where we selectively listen to one particular conversation in crowded room. Selective attention is studied in the laboratory by the “shadowing” technique.
8 Selective Attention Shadowing
10 Selective Attention One characteristic is that people speak with a very monotonous voice. Also they have very little idea of what the content of the message was - but of course they must have recognised each individual word in order to repeat it back. Interesting to ask in such experiments: how much of the rejected message is actually rejected?
11 Selective Attention In Cherry’s experiment participants had a message read in right ear (passages from newspapers) and shadowed the same ear. In the left ear in all conditions it started off with another normal message and then changed to one of 4 conditions….
12 Selective Attention Cherry (1953) In the left (unattended) ear: 1. No change - Normal male speech. 2. Changed to female speech. 3. Reversed male speech (same sound spectrum) 4. A steady tone.
13 Selective Attention Cherry (1953) - in the left unattended ear: 1. No change - Normal male speech. 2. Changed to female speech. 3. Reversed male speech (same sound spectrum) 4. A steady tone. Afterwards they asked questions e.g. was it human speech? Results: 1. Conditions 1 and 2 were recognised as speech every time - but couldn't even say if it was English. 2. Recognised as female speech 3. Thought to be strange by some, normal by others 4. Tone recognised by all
14 Selective Attention Moray (1959) looked at out how much information is retained in rejected channel or ear. He repeated certain words 35 times into this ear but absolutely no retention of words - even if told that they'd be tested later on their memory for rejected ear.
15 Selective Attention Monaural presentation means that two different messages are presented to one ear. If these two different messages are both presented to both ears - so that both ears hear exactly the same material, the presentation is “binaural”. Dichotic presentation means that the two channels are fed into the separate ears so that the left ear hears only one message and the right ear hears the other - as in Cherry's experiment - then the presentation is “dichotic”. Stereo presentation: each message is presented on two different loudspeakers.
16 Selective Attention: Problems with shadowing One problem is that it is far removed from the original cocktail party phenomenon. (We don't normally repeat back a conversation). It's repeating back that causes primary problem. 1. Verbal Interference a)Preventing rehearsal - using the vocal apparatus for shadowing prevents verbal rehearsal of the unshadowed message (Norman 1969). b)Masks sound - the sound of own voice masks rejected ear. Underwood & Moray (1971): males experienced more interference when they shadowed if both messages were in male voices compared with both in female voices. And same effect - but in reverse - for females.
17 Selective Attention: Problems with shadowing 2. Shadowing not sensitive to changes in attention Shadowing supposed to ensuring participant attending to message. But Dennis (1977): shadowing performance can remain unchanged under different levels of attention. His participants shadowed message at same time searched through word lists looking for semantic targets (e.g. furniture). He then tested their comprehension of the shadowed passage.
18 Selective Attention: Problems with shadowing 2. Shadowing not sensitive to changes in attention Denis (1977) found that during the demanding semantic target searching, comprehension performance was poorer than under less exacting circumstances searching for 'visual' targets e.g. letter T. But, interestingly, shadowing performance was not changed i.e. their level of uttering words was not changed even though attention had been affected by the semantic search task.
19 Selective Attention 3. Shadowing consumes resources One way to look at this problem is to compare between performances when participants shadow materials and when they just listen to materials. Typically, they demonstrate that performance in both channels is superior when participants just listen.
20 Selective Attention Beech and McKeating (1980): participants listened to radio plays. Two plays ran simultaneously with one in each ear, and participants had to attend to left ear. After questioned on content in their left ear. During the play, actors in the plays at random points said digits and if the participants heard a number in either ear pressed button. Another group of had to shadow the play in the left ear and the two groups were compared.
21 Selective Attention The table shows the percentage of digits detected in each ear Thus, when people shadowed, virtually no digits could be monitored in the unattended channel. However listeners detected 26% of digits in their right ear suggesting that about a quarter of the individual words streaming through their unattended ear were actually being monitored. Left ear (attended) Right ear (unattended) Shadowers75%1% Listeners90%26%
22 Selective Attention: Broadbent’s bottleneck theory An early theory of attention was proposed by Broadbent (1958). The basis for his theory was a “split span” experiment in which he gave participants 3 pairs of digits dichotically - in such a way that one member of each pair went to one ear at the same time as the other member went to the other ear.
23 Selective Attention: Broadbent’s bottleneck theory To left earTo right ear Time123 Digit pair
25 Selective Attention: Broadbent’s bottleneck theory At the slower rate participants reported digits paired together (LRLRLR). At the faster speed of ½ sec/pair then S's recalled spontaneously ear by ear i.e. LLLRRR. Broadbent concluded: selection of one message via the physical channel digit was presented - in this case the left ear or the right ear. Proposed: central limited capacity channel which filtered information. But this filter takes time to switch from one channel to next. Therefore participant couldn't alternate attention at fast speeds, one switch requiring.75 sec., according to Broadbent. Meanwhile message in other ear stored in an auditory short term store. While information in store, representation of message decays.
26 Selective Attention: Broadbent’s bottleneck theory
27 Selective Attention: Broadbent’s bottleneck theory Broadbent's basic hypothesis: Limited capacity processor can only deal with one channel of information at a time. Information chosen on basis of physical features such as intensity and pitch. Limitation of central processor is in terms of bits of information that person can handle per second. If information is low, system can cope with more than one channel. Selective Attention: Broadbent’s bottleneck theory
28 Selective Attention If the information is too much for system then filtering mechanisms are needed to prevent system from becoming too overloaded. Filters can be tuned by people to any of several channels e.g. the ears, eyes, smell, sense of touch etc.
29 Selective Attention Gray and Wedderburn (1960) conducted an experiment to test Broadbent's idea that attention was based on physical characteristics of sensory channels. They suggested that the rejected message might also be processed for its meaning. In their experiment, one word presented so that different syllables were presented alternately to different ears. At the same time another word is decomposed in a similar way and presented to the other ear.
31 Selective Attention Participants could do task. Suggests: meaning of both messages had to be extracted in order to know which message to select. Broadbent's system, proposes that switching occurs early on in processing, and is based purely on the physical characteristics of the message.
32 Selective Attention: Treisman’s attenuation theory
33 Treisman’s theory Anne Treisman (1961): the switch really an attenuator i.e. a mechanism that reduces information getting past, rather than shutting it off completely. To demonstrate: participants are shadowing one message and ignoring another in the other ear. Suddenly the 2 passages crossed over!
34 Treisman’s theory The messages switch ears at this point Left earSitting at a mahoganythree possibilities Right earLet us look at thesetable with her head
35 Treisman’s theory Messages analysed by filter for crude physical properties e.g. loudness, pitch, position, colour etc. Resulting information is available for reporting by participant. Filter also attenuates signal strength of output from these analysers. E.g. participant has to select only a female voice; filter will attenuate any signals that don't have this quality. Unweakened signal plus weakened signal(s) processed further via pattern recogniser (composed of large no. dictionary units). By travelling up a logical tree the components of the messages reach the end of their respective trees and each fire a dictionary unit.
36 Treisman’s theory Units have 2 properties: (a)Their thresholds differ e.g Unit firing own name has permanently lower threshold so that even if one's name is on attenuated message (i.e. the weakened signal), unit would still fire. (b)The thresholds are variable. Threshold differences between word units may be brought about by e.g. instructions to the participant ('listen out for articles of clothing') or by context.
37 Treisman’s theory Figure
38 Deutch & Deutch’s (1963) late filter theory They proposed a 'response selection' theory of selective attention. If one alters properties of dictionary, renders lower level filter irrelevant. At dictionary each signal is analysed and recognised. From there: to output mechanism which transmits to a level that participant becomes aware it. When signal input to dictionary it will fire according to how important stimulus is (changes in importance can be produced by context etc.) and extent of output activity from output mechanism is proportional to importance of the signal. The feature of this system is that messages analysed at earlier stage before the person is conscious of content.
39 Evidence against early selection (and for Deutch & Deutch) by MacKay (1973) Right ear Person says Left ear (half the group) Sentences with ambiguous meaning “Money” They threw stones toward the bank yesterday “River”
40 Evidence against early selection (and for Deutch & Deutch) by MacKay (1973) Phase 1– Sentences. They attended to their left ear and heard 28 ambiguous sentences and in the unattended ear one group heard e.g. “money” while the other heard e.g. “river”. Phase 2 – Recognition. All participants had to choose sentences that were the best match to those they’d heard: (a)“They threw stones toward the side of the river yesterday” (b) “They threw stones toward the savings and loan association yesterday”
41 Evidence against early selection (and for Deutch & Deutch) by MacKay (1973) Result Those who heard “money”in their unattended ear chose “financial institution” and those who heard “river” chose “river bank” They were asked about the word in the unattended ear and they were completely unaware of it. Conclusion The word in the unattended ear was processed for its meaning.
42 Selective Attention: parallel processing Visual attention Other techniques are being used to study attention. E.g.: Neisser & Becklen (1975) studied attention in the visual mode. Participants examined 2 optically superimposed video screens on which 2 different kinds of thing were happening. They had to follow the action in one episode - by pressing keys when significant events occurred e.g. in hand game the person pressed key every time an 'attacking stroke' made (whether or not it produced a hit) - and ignore the other.
43 Neissser & Becklen (1975) x
44 Selective Attention: parallel processing Visual attention People could do this without difficulty. However (as in shadowing task) very little information from the unattended film was processed. Neisser & Becklen (1975) proposed that it is highly improbable that special filters 'block out' irrelevant material. Also: people find it very difficult (or are unable) to process two things simultaneously in the same modality.
45 Selective Attention Broadbent's Model (dealt with before) In essence in the single channel hypothesis we deal only with one channel at a time. Information enters short term memory. The filter selects information on the basis of the physical features of the message e.g. intensity and pitch. The filter can be tuned to any of several channels e.g. the ears, eyes, smell, sense of touch etc. There is a limited capacity channel that can handle a certain number of bits of information/sec. If information load is too high, then the filtering mechanism operated to try to reduce the information. If information is low the p system (limited capacity channel) can handle several channels at once.
46 Selective Attention: parallel processing In other words: Broadbent's point was that as long as the two tasks that one is performing are low in information content (i.e. not very demanding on resources) one can do the two tasks simultaneously. Soon afterwards, as we've seen, Broadbent challenged on his ideas concerning a filter (e.g. Ann Treisman). It was argued that a certain amount of processing of rejected messages also takes place, and Treisman demonstrated this with some rather ingenious experiments. The part of Broadbent's model suggesting that the system cannot handle information if information load is too high challenged by Allport et al. (1972).
47 Selective Attention: parallel processing Allport et al. gave stimuli (1 every 3 sec) for 45 sec, then a one-minute rest, then test period showing originals + new, similar set. Participants either shadowed, or not. Stimuli were pictures, words- visual, words-auditory.
48 Selective Attention: parallel processing Allport et al. (1972) found that people can do things simultaneously in different modalities. For example, they could look at and remember pictures and shadow (ie. repeat back) at the same time without any problem. However, they couldn’t listen to single words in one ear and shadow the other ear at the same time – (similar to Cherry) – it is very difficult to do things simultaneously in the same modality.
49 Selective Attention: parallel processing Allport et al. (1972) in another experiment looked at the sight reading of music while shadowing and found that this was achieved relatively easily, but performance dipped when shadowing more difficult material (Norse poetry). So the information content does have a role to play.
50 Selective Attention: parallel processing Atwood’s (1971) model Atwood proposed that we have 2 separately operating modules (or systems) in which different operations can be done simultaneously as long as they are in the separate modules. But if we try to do two things in the same module then we experience problems. He proposed that the two systems were the visual system and the verbal auditory (VA) system.
51 Selective Attention: parallel processing Atwood’s (1971) model
52 Selective Attention: parallel processing Atwood (1971) gave 35 phrases (‘nudist devouring bird’) with 4 sec gaps between each phase. Then cued recall (‘nudist’ ____?). Phrases were concrete (told to image these) or abstract (‘Einstein was a genius’). Three types of interference: 1.none 2.visual (shown ‘1’ said ‘2’) 3.auditory (heard ‘1’ said ‘2’). 6 groups. Found…
53 Selective Attention: parallel processing - Atwood Type of interference (% correct) visualauditorynone Concrete phrases 58%76%82% Abstract phrases 60%44%70%
54 Selective Attention: parallel processing Criticisms of Atwood Concrete phrases more bizarre than abstract ones Atwood confounded instructional set with abstractness- concreteness of material i.e. visual imagery for concrete phrases, verbal processing for abstract phrases Lack of replication - mainly in unpublished studies (e.g. Brooks, Bower, Neisser, Janssen) Despite these problems, the Atwood model was a forerunner of more recent theories of modularity. Useful to take view that different modules can operate with some measure of independence of each other.
55 Meta-attention Meta-cognition is our ability to tune in or reflect upon our own mental processes. Thus meta-attention refers to our ability to introspect about the attention process. On one view attention is closely allied to consciousness. If we control our attention, we should be able to reflect upon it.
56 Meta-attention But we do make decisions reflecting use of subjective judgements about attention and performance (e.g. if academic work, might have radio on, but turn it off for other tasks). Reisberg and McLean (1985) examined effects of distraction on participants in terms of performance on the task and their subjective impressions of distraction.
57 Meta-attention Participants had to add up 10 numbers shown on a computer screen and distraction was recording of 1 minute of Joan Rivers. Their subjective impressions were monitored by asking the following 2 questions at the end of each of 20 trials: 1.How much of the distracting message did you feel that you heard? (0-100%) 2.How much did you feel disrupted by the presence of the distraction? (0-5 rating scale)
58 Meta-attention Reisber & McLean’s findings 1.The presence of a distractor slowed down responding to the main task 2.There was no association between response latency and reports of distraction, nor an association with how much the message was heard. People were hopeless in predicting their trial-by-trial performance. Thus material had significant distracting effect.
59 Meta-attention In next experiment included a financial reward for doing task and found that distracting effect virtually disappeared. However, there wasn't corresponding effect on self-report, because they reported being equally distracted by comedy tape as participants in previous group. Again, there's no relationship between actual performance and self-reports from trial-to-trial.
60 Meta-attention One explanation might be that participants don't actually have access to processes involved in producing performance. An implication might be: We find ourselves in situation in which we have to work but there are distractions, e.g. we might be in the library trying to work and someone is talking elsewhere. We might decide to try to deal with the distraction, however, our judgement of what is actually a distraction might be mistaken.
61 Meta-attention Hovey (1928) tried to use extreme distractors. There were 7 electrical bells, 4 buzzers, 2 organ pipes and 3 whistles, a circular saw, lively music, a spotlight flashing continuously; others entered noisily and strangely garbed, carrying strange apparatus. Nail kegs rolled up and down the aisles. Finding: these distractors worked only for short time while the participants were becoming adjusted to the situation. (Participants were compared with non-distracted group while both groups took on IQ test).
62 Meta-attention: Conclusion A paradox about distraction effects is very difficult to create artificially in lab., but in everyday life seems to occur so easily. In lab. distractors have to be quite high in distractibility such as stimuli of great personal importance (e.g. one's name) or inputs which conflict with a highly-learned response (e.g. the Stroop effect). But even when distractor found (e.g. comedy) can be overcome by giving participants sufficient inducements to concentrate. Where there is a will there is a way.