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Lecture 1

PSYC 1010 Lecture 1: SP Sept 30.pdf

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Department
Psychology
Course
PSYC 1010
Professor
Prof
Semester
Fall

Description
Sensation & Perception Modules 17, 18 & 19 • Information comes in through our senses • Our brains interpret this information – You LOOK with your eyes - You SEE with your brain • Sensation – Stimulus-detection process – Organs translate stimuli into nerve impulses • Perception – Organizing & giving meaning to input Absolute Threshold • Intensity at which a stimulus can be detected 50% of time – Lower the absolute threshold - Higher the sensitivity 1 Signal Detection Theory • How certain are we that a stimulus is present? • Criteria fluctuate • Apparent sensitivity fluctuates • Criteria changes depending on other factors • Fatigue, importance of stimulus, expectation • Ask participants to indicate if they perceived a stimulus (e.g., heard a tone) Difference Threshold • Smallest difference between 2 stimuli that can be detected 50% of the time – Just noticeable difference (JND) (Weber, 1830) • Weber’s Law – JND is proportional to magnitude of stimulus for which comparison is being made • Proportion is called Weber Fraction – Amount of increase needed to make a difference Sensory Processes • Sensory adaptation (habituation) – Diminishing sensitivity to unchanging stimulus – Occurs in all sensory modalities • Adaptive value – Frees senses from the unchanging to be more sensitive to changes in environment Vision • Perceive small part of electromagnetic (EM) spectrum • Light waves measured in nanometres (billionths of metre) – From 700 nm to 400 nm • Cornea Structures of the Visual Systems – Transparent protective structure • Pupil • Lens – Adjustable opening that controls – Elastic structure for focusing amount of light – Thinner to focus on distant objects – Thicker to focus on nearby objects • Retina – Photoreceptors transduce light energy into electrical impulses • Myopia - Nearsightedness • Difficulty seeing far away objects • Hyperopia - Farsightedness • Difficulty seeing close-up objects Photoreceptors • Located in retina – For colour and detail – Function best in high illumination – Concentrated in centre of retina – Fovea (in centre of retina) contains only cones – Function best in low illumination – 500 times more sensitive to light than cones – Found mostly in periphery of retina - though everywhere in retina except fovea Photoreceptors • Rods & cones have synaptic connections with bipolar cells • Axons of ganglion cells form optic nerves – Create ‘blind spot’ where optic nerve exits from eye • Transduction – Converting characteristics of stimulus to nerve impulses • Visual transduction – Action of photopigments – Absorption of light changes rate of neurotransmitter release – Greater rate of release = stronger the signal passed on Brightness & Dark Adaptation • Have ‘dual visual system’ – Human visual system adapted for both high & low light conditions – Progressive improvement in brightness sensitivity in low illumination • Rely on rods for vision in low light conditions • Rods & cones adapt differently Photoreceptors • Bipolar cells synapse with ganglion cells • Axons of ganglion cells form optic nerve –Create ‘blind spot’ where optic nerve exits from eye !"#$%&'()*+,-%.+)'/,+01##")2 !"#$%&'(#)$*#$+)##,$'-#$./0$&'1#$/2$3%("04$0"#5$ '-#$&'1#$/2$.#6-'3$)%(.'3)$*"%7"$7'.$8#$9-/167#1$ #:#.$85$9-#))6-#$/.$0"#$#5#8'33; $ :%)6'3$7/-0#?;0"-/6("$0"#$0"'3'&6)$0/$0"#$ /%,%&&1&'/,+01##")2 ! !6-.%.($3%("0$%.0/$0"#$.0'3$'70$/2$)##%.(@$ 3%("0$*':#)"7"#&%7'3$-#'7=/.)".#6-'3$%&963)#)"2#'06-#)"/8A#70)$ '.1$/.#$&/-#$)0#9;;;$ ! !"#"$$%$&'#()%**+,-&-#2#-)$0/$86%31%.($9#-7#9=/.)$/60$/2$)#.)/-5$ 1#0'%3)$9-/7#))#1$%.$1%B#-#.0$'-#')$/2$0"#$8-'%.;$ • Attaching meaning to what we see – Information goes to visual association cortex – Interpreted in terms of our memories & knowledge Trichromatic theory (Young-Helmholtz) – 3 types of colour receptors in retina – Cones most sensitive to blue, green, red wavelengths – Visual system combines activity from these cells – Colours are perceived by additive mixture of impulses – If all are equally activated - white colour is produced • Trichromatic theory cannot explain – Red-green colour blind individuals should not be able to perceive yellow (red + green = yellow) – Afterimages • Stare at red - look away you’ll see green (same for blue and yellow) 8 Colour Deficient Vision • Trichromats – Normal colour vision • Dichromats – Deficient in one system (red-green is most common) • Monochromat – Sensitive to black-white only Perception: Creation of Experience • 2 kinds of processing functions – Bottom up processing • Analysis of individual stimulus elements • Re-combines them into unified whole – Top-down processing • Use existing knowledge, concepts, ideas, expectations Role of Attention • Involves 2 processes –Focusing on certain stimuli –Filtering out other information Environmental & Personal Factors • Both play a role in attention • Stimulus characteristics – Intensity, novelty, movement, contrast, repetition • Internal factors – Motives, interests, threats to well being – Hansen (1989) showing groups of people. Perceptual Organization • Figure-Ground • What part of the image becomes the figure –bounded (closed) area –smaller area –symmetric area –convex area –brighter area • Gestalt = pattern, shape, form – Theorists argued wholes we perceive are more than sum of their parts • Suggested perception was governed by laws that determined how things were grouped together – Gestalt Laws of Perceptual Organization • Perceptual set Perception & Hypothesis Testing • readiness to perceive stimuli in particular way • based on expectations and prior information • creates psychological context to use in top-down processing Bird story Fish story Perceptual Constancies Recognize stimuli under varying conditions • Shape constancy • Brightness constancy • Size constancy Depth Perception • Monocular cues - Depth can be perceived with one eye • Binocular cues - Depth perceived with 2 eyes • Relative brightness • Interposition • Shade & shadow • Horizontal plane height • Size • Aerial Perspective • Linear Perspective • Texture density gradient Kinetic Cues Transformation of the retinal image from movement of the head or eyes • Motion parallax •
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