Lecture 3 - Race against Time 1 Three points for today Sensory memory (SM) contains highly transient information about the dynamic sensory array. Stabilizing the contents of SM allows identification of external stimuli, which in turn permits access to knowledge. Stabilization produces a new experience of world, that we call consciousness.

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Lecture 3 - Race against Time 3 1.The world and our representation of it.

Lecture 3 - Race against Time 4 The world and our representation of it A. External world Dynamic (in motion with respect to us). That is, something is always happening. B. Internal representation of the world Begins with receptor surface.

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Lecture 3 - Race against Time 6 Question Can the receptor surface drive all responses? That is, can any response be both prompted and guided only by information available at the receptor surface? E.g., shadow passing over squirrel causes squirrel to run for shelter – without thinking.

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Lecture 3 - Race against Time 8 Which behaviours could be driven by receptors? Responses based on distinctions available at receptors – e.g., for vision: light intensity wavelength (hue) contrast Nothing involving learning.

Lecture 3 - Race against Time 9 Which responses cannot be driven by receptors? Responses based on abstract properties – for vision, these properties would include: size shape category name These properties are computed based on information extracted from SM.

Lecture 3 - Race against Time 10 How do we extract information about objects from sensory memory? Two issues: 1. What is the nature of the stimulus representation? 2. How does the extraction process work? Which question is logically prior?

Lecture 3 - Race against Time 11 What is the nature of the stimulus representation? Three suggestions, in historical order: Template theory Feature theory Structural description theory

Lecture 3 - Race against Time 12 Template theory: memory contains pictures of (whole) objects stimulus representations are also pictures of objects recognition involves searching memory for picture that matches current stimulus representation.

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Lecture 3 - Race against Time 15 Problem with Template theory: How do you recognize objects at an unfamiliar orientation?

Lecture 3 - Race against Time 16 Feature theory: all visual objects are composed of features stored representations are lists of features stimulus representation created by extracting features from visual object recognition consists of matching feature sets

Lecture 3 - Race against Time 17 Problems with feature theory: 1.What are the features? nobody knows 2. What about spatial relations among features?

Lecture 3 - Race against Time 18 Chair?

Lecture 3 - Race against Time 19 Structural Descriptions A feature theory with spatial relations among features specified in description. Biederman’s Recognition by Components theory: Geons – geometric ions (primitives)

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Lecture 3 - Race against Time 21 In column B, the geons can be recovered, so the objects can be identified. Not so in column C.

Lecture 3 - Race against Time 22 How does the extraction process work? 1. Source - sensory memory Duration & capacity 2. Destination - short term memory 3. Rumelhart’s model

Lecture 3 - Race against Time 23 Sensory memory Sperling (1960) Tachistoscopic procedure - very brief exposure of a visual array - subject’s task is to report what’s in the array. - until Sperling, whole report technique used.

Lecture 3 - Race against Time 24 Whole report report all letters on screen 4 or 5 items out of 12 correct Were those 4 or 5 all there was in SM? Did the rest decay during “read-out?”

Lecture 3 - Race against Time 25 J V E C M B S A Y L K R “J – V – E – C – M” Theory 1 – that’s all we can get into SM: J V E C M

Lecture 3 - Race against Time 26 Theory 2 – rest of array decays during read-out: J V E C M B S A Y L K R “J – V – E – C – M” J V E C M B S A Y L K R

Lecture 3 - Race against Time 27 J V E C M B S A Y L K R “That’s all I remember…”

Lecture 3 - Race against Time 28 Sperling (1960) Partial report technique: After display disappears, a tone signals which row to report. Logic: if you can report a randomly selected row, you could have reported the other rows, too if a different tone had sounded.

Lecture 3 - Race against Time 29 J V E C M B S A Y L K R HearReport High tonetop row Medium tonemiddle row Low tonebottom row Note: delay between display offset and tone onset variable. Basic effect – delay = 0 msec.

Lecture 3 - Race against Time 30 Sperling’s results: 76% correct in partial report condition. A.Result suggests that most of a complex display is available in SM immediately after offset. B.76% of 4 letters = 3 letters. Why not 4 or 5 as in whole report condition? C. After 5 seconds, most of array has decayed.

Lecture 3 - Race against Time 31 Rumelhart’s model: Model of the extraction process that takes information from SM to STM. Explains Sperling’s results. Process operates in parallel on all contents of SM (unless task instructions say focus). Process influenced by stimulus quality – better quality, faster process.

Lecture 3 - Race against Time 32 J V E C M B S A Y L K R Process operates in parallel. Process influenced by stimulus quality.

Lecture 3 - Race against Time 33 As a result, we can recognize thousands of objects. We have many possible responses to each object. How do we select: which object we should respond to? which response to that object we should carry out?

Lecture 3 - Race against Time 34 Selection is the responsibility of attention – see next chapter. But note: William James: Selection is the function of consciousness. Consciousness refers to experiencing the world.

Lecture 3 - Race against Time 35 Which comes first? Do we have consciousness because we have stable representations? Or do we have stable representations because we have consciousness (so are able to choose objects and responses)?

Lecture 3 - Race against Time 36 Quick evaluation: On a piece of paper, please write down one or two sentences about each of: What you liked best about today’s lecture. What you still have some confusion about. Be constructive – but don’t put your name on the paper! (Please hand it in as you leave.)