Chapter 1 in Chaudhuri Basic Concepts in Perception

Basic Concepts in Perception

The Process of Perception & Methods for Measuring Simple Perceptions

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Structure of Course

Somatosensory

Chemosensory

Smell

Taste

Audition

Vision

Stimulus

Pressure, heat/ cold, vibration...

Chemical odorants

Chemical tastants

Sound waves

Light

Sense Organ

The skin (& other epithelials)

Olfactory mucosa

Tongue

Outer, middle, & inner ear

Eye, retina.

Sensory Transducer

Mechano/ Thermo/Noci

receptors

Olfactory sensory neurons

Taste Buds

Hair cells Rods & Cones

Neural Processing

Medial Lemniscal vs. DorsolateraI.

VPN, S1, S11, etc.

Olfactory bulb, O1

3 taste-carrying nerves, NoST,

VPM, POC

Auditory Nerve CN, SON, IC, MGN,A1, etc.

Optic Nerve, LGN, SC,V1,

etc. etc.

Higher-order perception

Haptic object recognition,

illusions

Pheromonal effects

Flavour

Auditory scene

Object

analysis, pitch recognition

Touch,

Modalities temperature,

???

motion

Sour, sweet, bitter, salty,

savoury

Pitch, amplitude, source location

Spatial vision, motion, colour,

depth

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Basic Concepts in Perception

Chapter 1 in Chaudhuri

? Why study perception? ? Methods in perception research ? Measuring perceptions quantitatively

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Why Study Perception?

? Future careers: Graduate school work in perception, cognition etc.; clinical areas too.

? Applies to many other areas (design, graphic arts, intelligent systems programming...)

? Understanding the immense intricacy of the sensory systems

? Because it is very very cool! (yes, I'm biased)

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Schizophrenia & Smooth Pursuit Eye Movements

Perception & IQ

See, e.g., Holahan ALV, O'Driscoll GA.. Schizophrenia Research, 2005, 76, 43-54.

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The Importance of Perception

? "Man is nothing more than a bundle of sensations" --Protagoras, 450 B.C.

? Virtually everything you know, you know ultimately because of a sensory input.

? Scientific knowledge is entirely dependent on the perceptions of scientists.

? Perception seems simple and direct, but it is in fact fiendishly complex and very indirect.

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Baltes P.B., & Lindenberger, U. (1997). Psychology and Aging, 12, 12-21.

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Na?ve Realism

? The philosophical POV that sensation is simple and direct "I see it because it is there"

? Illusions, among other things prove that this is incorrect

? Research has shown that our sensory systems use complex heuristics to give us a percept of the world that is limited.

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? The moon illusion is one example of illusions that we experience around us on an everyday basis.

? The moon looks bigger on the horizon, even though it is in fact the same size and at the same distance.

? This is not an atmospheric lensing effect ? For more on this and many other illusions:



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Questions

? What are some reasons for studying perception?

? Give an example of how perception applies to other fields.

? Define "na?ve realism".Why is it untenable?

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Sensation vs. Perception

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Methods in Perception Research

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Methods in Perception

? Qualitative: Getting the big picture. ? Quantitative: Understanding the details ? Threshold-seeking methods ? Magnitude estimation ? Many others, often similar to those used in

other areas of psych.

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Qualitative Methods in Perception

? Also called phenomenological or naturalistic observation methods

? Relatively non-systematic observation of a given perceptual phenomenon or environment (e.g., an illusion)

? Yields a verbal description of one's observations, (possibly with some simple numerical assessment)

? First step in any study of any perceptual phenomenon. Gives the "big picture"

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Qualitative Observation

? "Thatcher Illusion" ? Qualitative observation

uncovered the phenomenon

? Much quantitative work now trying to find out why it happens & what it means

Schwaninger, A., Carbon, C.C., & Leder, H. (2003). Expert face processing: Specialization and constraints. In G. Schwarzer & H. Leder (Eds.), Development of Face Processing, pp. 81-97. G?ttingen: Hogrefe.

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Qualitative Methods in Perception

? Example: Famous perception researcher Jan Purkinje noticed that his flower bed looked light red/dark green during the day but dark red/light green at twilight

? This phenomenological observation led to the hypothesis of 2 visual systems, & ultimately to an understanding of the functions of rods and cones

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Quantitative Methods

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Quantitative Methods in Perception

? Threshold seeking methods measure a physical quantity representing a limit of perceptual ability (i.e., a threshold)

? Measured in physical units (meters, decibels, parts-per-million, candelas of light, etc.) ? Absolute threshold - smallest detectable physical quantity (e.g., 2 dB, 3.57 grams...) ? Difference threshold - smallest detectable difference between two physical quantities

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Quantitative Methods in Perception

? Thresholds are defined for a given level of response accuracy

? Typically we speak of the "50% threshold", meaning the physical quantity detectable (absolute threshold) or the physical difference detectable (difference threshold) 50% of the time

? But a threshold can be defined for any level of accuracy (e.g., 75%, 83.6%...)

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Threshold-seeking Methods

? Classic methods (Fechner, 1850's) ? Method of adjustment: Quick and dirty ? Method of limits: Easy on observer, fairly

fast and accurate

? Method of constant stimuli:Very slow but very accurate

? Adaptive methods: Fast, very accurate, but can be difficult for untrained observers

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Method of Adjustment

Adjustment

Constant Stim.

Method of Adjustment

? Stimulus intensity is adjusted (usually by the observer) continuously until observer says he can just detect it

? Threshold is point to which observer adjusts the intensity

? Repeated trials averaged for threshold ? Fast, but not always accurate, due to

inherently subjective nature of adjustment

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Method of Adjustment

Instructions: Adjust the intensity of the light using the slider until you can just barely see it

Collin, C.A., Therrien, M., Martin, C., & Rainville, S.J.M. (2006). Spatial frequency thresholds for face recognition when comparison faces are filtered and unfiltered. Perception & Psychophysics, 68, 879-889.

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Photometer Reading: 0.987654321 cd/m2

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Points of Subjective Equality (PSEs)

? Threshold-seeking methods can also be used to find PSEs.

? The PSE is the level of a physical characteristic of a stimulus at which it appears similar to another stimulus.

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Points of Subjective Equality (PSEs)

? PSEs can be used to (among other things) quantify the strength of an illusion

? Example: If the lower figure has to be 1.2 times the length of the upper one to appear equal, then we can say that under these circumstances the illusion has a 20% effect.

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Method of Adjustment for PSE

Instructions: Adjust the length of the lower figure until it appears to be the same length as the upper (standard) stimulus

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Method of Limits

? Stimuli of different intensities presented in ascending and descending order

? Observer responds to whether she perceived the stimulus

? Cross-over point (between "yes, I see it" and "no, I don't") is the threshold for a sequence

? Average of cross-over points from several ascending and descending sequences is taken to obtain final threshold. 28 28

Method of Limits (descending sequence) Instructions: For each light intensity, indicate whether you can detect it.

Photometer Reading: 0.98765432 cd/m2

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Example Data From Method of Limits

? Why ascending and descending sequences?

? Why different starting points?

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Method of Limits (ascending sequence) Instructions: For each light intensity, indicate whether you can detect it.

Photometer Reading: 0.98765432 cd/m2

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Method of Constant Stimuli

? 5 to 9 stimuli of different intensities are presented many times each, in random order

? The intensities must span the threshold, so must know approx. where it is a priori.

? Multiple trials (often 100's) of each intensity are presented

? Threshold is the intensity that results in detection in 50% of trials

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