SENSATION AND PERCEPTION Is everything that’s around us really there?

Sensation v. Perception The passive process of bringing information from the outside world into the body and the brain The active process of selecting, organizing, and interpreting the information brought to the brain by the senses.

Sensory Systems Information is acquired and then TRANSDUCED

Thresholds ABSOLUTE THRESHOLD – minimum magnitude of a stimulus that can be discriminated from nothing. DIFFERENCE THRESHOLD (jnd) – minimum difference in stimulus needed to tell stimuli apart WEBER FRACTION – intensity increased/intensity of the standard 100 candles burning – you need to add 8 more candles to notice the difference: 8/100 = 8%

Signal Detection Theory The detection of a stimulus involves a decision making process in addition to the sensory one. Bias influences the rate of observer detection.

Sensory Coding First step to sensation process is activation of receptors that transduce sensory info. The electrical message then goes to different areas in the brain. Penfield (1950) – electrically stimulated parietal lobes of surgery patients. They reported experiencing sensation of feeling. Intensity of sensation is primarily the result of the number of neural impulses…we’ll come back to this in more depth later

VISION

Cornea – protective covering (light enters the eye at this point); focuses the light Pupil – allows light into the eye (dilates and contracts) Iris – muscle that controls the pupil Lens – helps to focus the light (image is inverted) Retina – layer of tissue that contains receptor cells (where transduction takes place) Rods – specialized for seeing at night Cones – specialized for seeing during the day Fovea – center of the retina (high visual acuity = lots of cones) Blind spot – where the optic nerve leaves the eye (no receptor cells)

Seeing light Cones are more important to visual acuity Dark adaptation Pupil changes size Photochemical changes in receptors’ sensitivity to light Visual acuity – eye’s ability to resolve details

Color Vision Color is the result of differing light wavelengths (except…) Color mixing (red, blue, green) can create any hue Suggests that information is actually lost Suggests explanation for colorblindness Monochromat and Dichromats

Theories on Color Young Helmholtz Theory (Trichromatic) Retina has three color receptors that correspond to the primary colors Joint action of the receptors determines color Different types of cones receive light of differing wavelengths Opponent Color Theory Have you ever seen a reddish green? A yellowish blue? Opponent pairs of colors – cannot be seen simultaneously Color opponent cells in the thalamus respond to different wavelengths

Audition

Middle Ear Eardrum – membrane that vibrates Malleus, Incus, Stapes – bones that vibrate the next membrane (oval window) Inner Ear Cochlea – coiled bone that contains the auditory receptors, filled with fluid Basilar Membrane – section of cochlea that contain “hair cells”

Hearing Loss Conduction loss Poor conduction in the middle ear – requires greater frequencies Sensory-neural loss Inner ear damage (hair cells are unable to regenerate)

Hearing Pitch Temporal Theory Frequency of stimulus creates vibration of the entire basilar membrane which causes us to hear a specific pitch. Place Theory Each place along the basilar membrane corresponds to a pitch sensation.

Olfaction Animals use smell to communicate much more than humans Pheremones Receptors in nasal passage Cilia in nasal passage transduce the message Travels to the olfactory bulb, then to cortex on temporal lobes Human sensitivity to smell is much lower than many animals

Gustation Experience greatly affects taste Stimulus is what is dissolved in saliva, taste buds are the receptors Connection between cognition and taste and smell – Plassmann et al (2008)

Pain Phasic pain – immediate Tonic pain – long lasting Culture/Experience play a role in the perception of pain Gate Control Theory – a neural gate in spinal cord allows pain messages to travel to the brain

Perception Model of the environment Perception not only involves environmental stimuli, but also automatic and deliberate processes based on assumptions, expectations, and ways of thinking 1. Attention 2. Location 3. Identification 4. Abstract what is critical 5. Constancy

Attention We are exposed to many stimuli at all times, but we really only remember information that draws our attention. Attention is multimodal – moves within a single modality, as well as across multiple. So, is this a good or a bad thing?

Inattention/Change Blindness

Localization Figure and Ground – visualize stimulus in these two regions Grouping – we see patterns as going together

Distance Perception Binocular Cues – using both eyes Binocular Disparity – difference in the views seen by each eye Monocular Cues – using a single eye Relative Size Interposition Relative Height PerspectiveShadingMotion

Stroboscopic vs. Real Motion Images appear on different parts of our retina simultaneously An image moves across our retina

Recognition Role of the environment – global to local Stages of recognition – primitive, and then more complex? Feature detectors – we have single cells whose role it is to detect primitive features Top down processing – driven by knowledge/experience Bottom up processing – driven by the input Prosopagnosia – inability to recognize faces (but can recognize other objects)

Perceptual Constancy Constancy is the ability to perceive something as consistent even if the stimulus changes Color constancy – perceive the reflectance characteristic no matter the light wavelength Brightness constancy – lightness of an object changes little even when intensity is changed Shape constancy – perceived shape is constant even though retina image changes Size constancy – size remains constant no matter the distance

Moon Illusion Moon on horizon looks significantly larger than in the sky. Brain interprets its size as shrinking as it rises because it judges that the retinal image should really increase (but it doesn’t)

Ames room Size constancy isn’t working Lines of the room lead us to believe that it’s normal, when it’s really not

Which scary guy is bigger?

Perceptual Development Infant studies Preferential looking method Habituation Visual acuity in infants is low for the first few months – it picks up at 6 months and by age 2 is at adult levels Depth perception is not fully developed until 6 months (visual cliff)

Controlled development When animals denied light early on it not only inhibited their ability to discriminate patterns, but actually caused nerve cells to die off Kittens raised in environment of only vertical stripes become blind to the stimulus to which they were not exposed Critical period? Active perception adds to development – 2 kitten study