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PSYA01H3 (1,196)
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Chapter 4

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University of Toronto Scarborough
Steve Joordens

Chapter 4: Lecture 11- Sensation & Perception: Subliminal Perception Weber Flashback! Just Noticeable Differences - Earnst weber: the real pioneer of psychophysics - His goal was to study how the external world is represented into the human mind - Wanted to find the link between the external world and our perception of it Difference vs. Absolute Thresholds - Weber’s technique was all about finding difference thresholds … the point where participants can notice a difference - But what we’d really like to know is how sensitive our sensory systems are … that is, what is the weakest stimulus they are sensitive to … what is their absolute threshold - When you cross the threshold, something changes - Threshold: the point where you don’t see, feel, taste, smell, then suddenly you do. - How do we measure this? That is the challenge we want to figure out Subliminal perception - Maybe if we talk to subconscious, we can find an efficient way to modify behaviour Subliminal Seduction! Signal Detection Theory. Typical Experimental Context - Something is presented and you are asked if you saw anything, yes or no - Third no: a miss. Stimulus was presented but the person didn’t see anything - Last yes: nothing was presented by person said they saw something… called a false alarm Signal Detection Theory Terminology - In an trial a stimulus could be present or absent - A person could respond yes or no - The 4 types of trials we end up with - When there is a trial and a person says yes: HIT - Says no: MISS - Present: Hit 7/10= .70 = miss 3/10= 0.3 - Absent: False alarm 2/10= .2 = Correct Negative = 8/10=0.8 - - SDT: The Logic, Step 1 SDT: The Logic, Step 2 SDT: The Logic, Step 2 So is Subliminal Perception Real? Lecture 12: Vision Sensation Perception vs. Sensation - THC messes with associated cortex The Limits of Sensation - Humans do not sense all there is to sense; - bats have echo-location, sharks sense minute electrical currents, rattlesnakes are sensitive to low frequency vibrations, dogs can smell cancer - Dogs know who was in the room before - Vision is about transducing light into perception The eye Iris - The colored part of your eye … it is actually a muscle that controls the size of the pupil. Pupil - The black part in the middle of the eye … the opening that allows light into the eyeball … lights out! Sclera - The white part of the eye … a tough membrane that serves as protection Cornea - The fluid filled outer coating of the eye … provides moisture and nutrients Lens – Focuses the incoming light onto the retina. This lens is flexible and slight alterations in it can alter the focus of it, a process called accommodation (as an example, squint). Aqueous Humor - This fluid nourishes the front of the eye Vitreous Humor - This fluid nourishes and supports the inner part of the eye Retina – The surface that the image lands on. The inner coating is the retina is the part that transmits the light signal (focused or not) into a neural signal. Transduction - Sensory Neurons play the critical role of translating the physical properties of the outside world into neural signals … a process termed transduction - goes from physical stimulus to sensory(turns into action potentials that go and travel through the brain) - perception can induce behaviour Visual Transduction Photoreceptors – Rods and Cones (Transduction proper – Red, Green, Blue) Bipolar Cells – Image sharpening, edges and contours made crisper Ganglion Cells – Colour sharpening, and introduction of yellow) Photoreceptors - Light strikes the back of the eye stimulating photoreceptor cells which can be either rods or cones (show overhead). - Rods are not responsive to colour, but they are very responsive to dim light … great for low light situations. - Cones are sensitive to colour (red, green and blue) and provide a much more detailed image … great for high light, detailed imaging. - The transduction is done via a bleaching process in which the photo-pigments are split, causing an action potential. - Where transduction happens - -Eye works backwards from how a computer works Red, blue and green mix to produce a certain colour that you see (computer) Bi-Polar Cells - The signal from the photoreceptors is then passed on to the bipolar cells which reprocess the signal in a way that tends to emphasize edges and contours. - Essentially, when the photoreceptors associated with spatially close parts of the retina are sending very different signals, the bipolar cells accentuate these spots aiding us in our ability to perceive edges. Ganglion Cells - Help sharpen colours, use an interesting cell called an opponent process cell - When ganglion cells are resting, it fires at a middle rate. - They come in two types, red/green and blue/yellow - The rate increases when red is present, and decreases when green is present. - When there is none there is a mid-level rate, and if both colours as well. - Equal amount of red and green stimulates yellow - Yellow kind of becomes for a while red and green, if blue is present it slows down Lecture 13: Vision: Perception Perception vs. Sensation - Top-down perception, what is this? - When people say bottom up they mean the raw input from the world coming in through the senses, top down our brain right at the moment input is coming in, our brain is expecting certain stuff, so it is exerting an influence right from the beginning that will determine how we percieve what we perceive, brain (top) - Brain influence is top down, raw input is bottom up 12 13 14, A B C (this is the top down, it is perceived different) - Flipping the cube, psychologically a hard thing to describe Takes effort to hold it in that flipped way - Interesting aspect is its not really context, its different from the previous, its just your mind,
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