Sensory Perception PDF

Sensory Perception Visual Cues • When we look at something, we need to make inferences Visual cues allows us to perceptually organize by taking into account the following cues: depth, form, motion, constancy Humans have two eyes which allow them to receive visual cues from their environment by bin...

Sensory Perception Visual Cues • When we look at something, we need to make inferences Visual cues allows us to perceptually organize by taking into account the following cues: depth, form, motion, constancy Humans have two eyes which allow them to receive visual cues from their environment by binocular cues. These give them a sense of depth. o This gives them retinal disparity. Eyes are ~2.5 inches apart which allows humans to get slightly different views of objects of world around. Gives humans an idea on depth. • o Convergence: Gives humans an idea of depth as well based on how much eyeballs are turned. Gives humans a sense of depth. § Things far away – muscles of eyes relaxed. § Things close to us – muscles of eyes contract. Humans also have visual cues they receive which they do not need two eyes for. These are monocular cues. o These give humans a sense of form of an object § Relative size- Can infer with one eye. The closer an object it is perceived as being bigger. Gives us an idea of form. • • 8 § Interposition (overlap)- Perception that one object is in front of another. An object that is in the front is closer. § Relative height- things higher are perceived to be farther away than those that are lower. § Shading and contour- using light and shadows to perceive form depth/contours – crater/mountain. o Monocular cues can also give a sense of motion § Motion parallax- “relative motion” Things farther away move slower, closer moves faster. o Monocular cue of constancy § Constancy – Our perception of object doesn’t change even if the image cast on the retina is different. Different types of constancy include size constancy, shape constancy, color constancy. • Size Constancy: One that appears larger because its closer, we still think it is the same size. • Shape Constancy: a changing shape still maintains the same shape perception. 9 • o Ex. A door opening means the shape is changing. But we still believe the door a rectangle Color Constancy: despite changes in lighting which change the image color falling on our retina, we understand (perceive) that the object is the same color. Sensory Adaptation • Sensory adaptation: Our senses are adaptable and they can change their sensitivity to stimuli. o Hearing adaptation - inner ear muscle: higher noise = muscle contract (this dampens vibrations in inner ear, protects ear drum.) Takes a few seconds to kick in! So does not work for immediate noises like a gun shot, but it works for being at a rock concert for an entire afternoon o Touch - temperature receptors desensitized over time. o Smell – desensitized receptors in your nose to molecule sensory information over time. o Proprioception – is the sense of the position of the body in space i.e. “sense of balance/where you are in space.” § Experiment: goggles that make everything upside down and the perception of the world, and eventually you would accommodate over time, and flip it back over. o Sight – down regulation or up regulation to light intensity. § Down regulation: light adaptation. When it is bright out, pupils constrict (less light enters back of eye), and the desensitization of rods and cones become desensitized to light) § Up regulation: dark regulation. Pupils dilate-, rods and cones start synthesizing light sensitive molecules Weber’s Law • • • • • • • 2 vs. 2.05 lb weight feel the same. 2 vs. 2.2 lb weight difference would be noticeable. The threshold at which you’re able to notice a change in any sensation is the just noticeable difference (JND) So now take 5 lb weight, in this case if you replace by 5.2 weight, might not be noticeable. But if you take a 5.5 lb it is noticeable. I = initial intensity of stimulus (2 or 5 lb), ΔI = JND (0.2 or 0.5). Thus, Weber’s Law is: o ΔI (JND)/I (initial intensity) = k (constant) o ex. 0.2/2 = 0.5/5 = 0.1, change must be 0.1 of initial intensity to be noticeable If we take Weber’s Law and rearrange it, we can see that it predicts a linear relationship between incremental threshold and background intensity. 10 o ΔI = Ik. o If you plot I against ΔI it’s constant Absolute Threshold of Sensation • Absolute threshold of sensation: The minimum intensity of stimulus needed to detect a particular stimulus 50% of the time. • At low levels of stimulus, some subjects can detect and some can’t. Also there are differences in an individual. Not the same as the difference threshold (JND – Just Noticeable Difference) – that’s the smallest difference that can be detected 50% of the time. Related but different concepts. Absolute threshold can be influenced by a # of factors. Not a fixed unchanging number. Particularly, it is influenced by a variety of Psychological states. o Expectations – ex. Are you expecting a text. o Experience (how familiar you are with it) – ex. Are you familiar of the phones text vibration sound. o Motivation – ex. Are you interested in the response of the text o Alertness – Are you awake our drowsy. Ex. You will notice text if you are awake Subliminal stimuli – stimuli below the absolute threshold of sensation. • • • Somatosensation • • • Receive information about the types of somatosensation, the Intensity, Timing, and Location Types: Temperature (thermoception), pressure (mechanoception), pain (nociception), and position (proprioception) Intensity – how quickly neurons fire for us to notice. Slow = low intensity, fast = high intensity. 11 • • Timing: Neuron encodes 3 ways for timing: non adapting, fast adapting, or slow adapting o Non-adapting- neuron consistency fires at a constant rate o Slow-adapting - neuron fires in beginning of stimulus and calms down after a while o Fast-adapting - neuron fires as soon as stimulus start…then stops firing. Starts again when stim stops). Location: Location-specific stimuli by nerves are sent to brain. Relies on dermatomes. *Note: This graph doesn’t relate rows to columns, read columns separately The Vestibular System • • • • • • A type of sensation. Balance and spatial orientation Comes from both inner ear and limbs. Focus on inner ear - in particular the semicircular canals (posterior, lateral, and anterior; each orthogonal to each other) Canal is filled with endolymph, and when we rotate the fluid shifts in the semicircular canals – allows us to detect what direction our head is moving in, and because we can detect how quickly the endolymph is moving we can determine the strength of rotation. Otolithic organs (utricle and saccule) help us to detect linear acceleration and head positioning. In these are CaCO3 (Calcium carbonate) crystals attached to hair cells in viscous gel. If we go from lying down to standing up, they move, and pull on hair cells, which triggers AP. These would not work very well w/o gravity! Buoyancy can have effects as well, particularly without visual cues on which way is up/down. Also contribute to dizziness and vertigo (when you or objects around you are moving when they are not) o Endolymph doesn’t stop spinning the same time as we do, so it continues moving and indicates to brain we’re still moving even when we’ve stopped – results in feeling of dizziness. 12 Signal Detection Theory – Part 1 • • Signal Detection Theory: Looks at how we make decision under conditions of uncertainty – discerning between important stimuli and unimportant “noise” At what point can we detect a signal o Origins in sonar – is signal a small fish vs. large whale. o Its role in psychology – Imagine being given a list. Then a second list. Now experimenter asks, which words on the second list were on the first. Person has to have uncertainty as they are not sure whether a certain word is exact or similar than the one in the first list. (Which words on second list were present on first list.) o Real world example – traffic lights. It’s foggy day & you have to decide when to start driving. How strong does a signal have to be for you to drive? Signal is present or absent (red). o Options: hit/miss/false alarm/correct rejection § Hit, the subject responded affirmative when a signal was present, § False Alarm, the subject perceived a signal when there was none present; § Correct Rejection, a correct negative answer for no signal § Miss, a negative response to a present signal 13 *Note: Do not mistake this for Type I/Type II errors. This is different terminology. • Strength of a signal is variable d’, and c is strategy o d’: Strength § hit > miss (when there is a strong signal), § miss > hit (weak signal) o c: strategy § 2 strategies • Conservative strategy - always say no unless 100% sure signal is present. Bad thing is might get some misses. • Or liberal strategy- always say yes, even if get false alarms. Signal Detection Theory – Part 2 • For any signal, have noise distribution (background). And get a second graph – the signal distribution. o The difference between means of the two is d’. So if signal shifted to right, d’ would be big and easy to detect. If left, d’ very small and more difficult to detect. o X-axis has intensity. o The strategy C can be expressed via choice of threshold – what threshold individual deems as necessary for them to say Yes vs. No. Ex. B, D, C, beta, just diff variables. o If we were to use the strategy B, let’s say choose this threshold à 2. So anything > 2 will say Yes, anything <2, say No. So probability of hit is shaded yellow, and false alarm is purple. o D strategy: D = (d’- B), so let’s say d’ in this example is 1, so 2-1=-1. So if we use D strategy, anything above -1 = Yes; anything below -1 = No. o C strategy is an ideal observer. Minimizes miss and false alarm. C = B – d’/2. So in our example, it’s 2- ½ = 1.5. So anything above a 1.5 is YES, anything below 1.5 is NO. § When C = 0, participant is ideal observer. If <1 à liberal. If >1 à conservative. o Beta strategy: set value of threshold to the ratio of height of signal distribution to height of noise distribution, i.e. ln beta = d’ x C = 1 x 1.5 = 1.5. So e^1.5 = beta = 4.48. 14 Bottom-Up vs. Top-Down Processing • • Bottom up Processing: Begins with stimulus. Stimulus influences what we perceive (our perception). o No preconceived cognitive constructs of the stimulus (never seen it before) o Data driven. And the stimulus directs cognitive awareness of what you’re looking at (object) o Inductive Reasoning. Always correct. Top-down Processing: uses background knowledge influences perception. Ex. Where’s waldo o Theory driven. Perception influenced by our expectation o Deductive Reasoning o ex. creating a cube when it’s not there! Not always correct. Gestalt Principles • • Gestalt Principles (i.e. Gestalt’s Laws of Grouping): Tries to explain how we perceive things the way we do. o Imagine watching a basketball game on TV. Why don’t we tell ourselves that we’re looking at bunch of still pictures rather influence ourselves that it’s some fluid realistic representation of basketball game? Similarity: items similar to one another grouped together by brain. Ex: The brain automatically organizes these squares and circles in columns, and not in rows. 15 • Pragnanz: reality organized reduced to simplest form possible. Ex. Olympic rings, where the brain automatically organizes these into 5 circles, instead of more complex shapes. • Proximity: objects that are close are grouped together, we naturally group the closer things together rather than things that are farther apart. Ex: We group things close to one another together. • Continuity: lines are seen as following the smoothest path. Ex: You group the line together! • Closure: objects grouped together are seen as a whole. Mind fills in missing information. Ex. You fill in the triangle even though there is none. 16 • Symmetry: the mind perceives objects as being symmetrical and forming around a center point. • Law of Common Fate: For example, if there are an array of dots and half the dots are moving upward while the other half are moving downward, we would perceive the upward moving dots and the downward moving dots as two distinct units. Law of Past Experiences: The law of past experience implies that under some circumstances visual stimuli are categorized according to past experience. If two objects tend to be observed within close proximity, or small temporal intervals, the objects are more likely to be perceived together. For example, the English language contains 26 letters that are grouped to form words using a set of rules. If an individual reads an English word they have never seen, they use the law of past experience to interpret the letters "L" and "I" as two letters beside each other, rather than using the law of closure to combine the letters and interpret the object as an uppercase U Contextual Effects: the context in which stimuli are presented and the processes of perceptual organization contribute to how people perceive those stimuli (and also that the context can establish the way in which stimuli are organized) • • Sight (Vision) Structure of the Eye • • Conjunctiva: thin layer of cells that lines the inside of your eyelids from the eye. Cornea: transparent thick sheet of fibrous tissue, anterior 1/6th; starts to bends light, first part of eye light hits. 17