2/28: Sensation

• Sensation: process by which our nervous system receives and represents stimuli from the environment
• sensory receptors absorb raw physical energy
• raw energy transformed into neural signals which are sent to the brain
• Perception: organizing and interpreting sensory information, enabling us to recognize meaningful objects and events
• meaning assigned to sensory information
• Attention---Memory----Thinking Action = Sensation ; Thinking Action---Memory--Attention= Perception
• simultaneous processes
• Bottom-up, Attention to Thinking Action, = Sensation
• Top-down, Thinking Action to Attention = Perception

Sensation - Thresholds

• Sensation
• subjective and cannot be measured using objective instruments
• evaluated using psychoanalysis
• Absolute Threshold: minimum stimulation needed to detect a particular stimulus 50% of the time
• vary with age
• Signal Detection Theory: understand why people respond differently to same stimuli and why the same people reactions change in different circumstances
• detecting a stimulus is determined by the signal and the subject's criterion (bias)
• Just Noticeable Difference (JND)
• definition: minimum difference a person can detect between any two stimuli  half the time
• Weber's Law: JND is a function of proportions
• Subliminal messages:
• definition: words and pictures not consciously perceived that are supposedly influence behavior and judgment and attitudes
• FCC banned use of subliminal messages
• no control group in movie theater study
• No evidence of subliminal messages used in everyday life have any influence on behavior
• Greenwald (1991): study on subliminal messages
• Results: neither of tapes had any effect on people's memory or self-esteem
• sensation
• Person thinks self-esteem tape but really listen to memory tape, increase in memory
• perception
• Sensation: Vision
• seeing light = pulses of electromagnetic waves hitting eyes
• Frequency of color
• wavelength = type of color
• short = high frequency bluish colors
• long = low frequency reddish colors
• amplitude = intensity
• great = bright colors
• small = dull colors
• Sensation: The Eye
• Cornea
• light enters through here
• protects eye
• bends light to provide focues
• Pupil
• small adjustable opening
• size regulated by the Iris- a colored muscle surrounding the pupil
• Lens
• fine-tunes focusing of light
• Retina
• light sensitive surface on which rays focus
• images projected upside down 
• Acuity - sharpness of vision
• Nearsightedness: images of far objects is focused before the retina
• Farsightedness: image of near objects is focused behind retina
• Retina contains millions of photoreceptor cells that convert light energy into neural activity
• Rods: sensivitee to light
• Cones: sensitive to color
• Rods vs Cones
• Rods
• concentrated at the outer edge of the retina
• share bipolar cells with other rods = combined messages
• not good at precise information
• perceived black and white
• sensitive in dim light
• Cones
• clustered in the fovea
• direct connection to cortex via bipolar cell
• better at precise info
• perceive color
• ineffectual in dim light
• types
• red 
• green
• blue
• combo of types = multiple colors
• colorblindness
• one of cones not working
• Parallel Processing
• brain cell teams process combined info about
•  color, motion, form, depth
• Recognition-----Retinal Processing------Feature Detection

Hearing

• Sound
• waves as vibrations
• pattern of rapid wavelike movements of air molecules
• movement jolts surrounding air molecules and these collide with others
• 750 mph
• much slower than light
• travels in waves
• wavelength = pitch/type of sound
• short = high frequency/ high pitched sounds
• long = low frequency/ low pitched sounds
• frequency = intensity
• great = loud
• small = soft
• Process
• Collected in Outer Ear
• Auditory canal ----Eardrum
• Eardrum Vibrates Bones in Middle Ear
• Vibrations cause Hair Cell movements send neural message---- Auditory Cortex
• Locating Sound
• detection small differences between right and left ear
• measures just noticeable difference
• Hearing Loss
• Conduction Hearing Loss: caused by damage to the mechanical system of the ear
• Sensorinerual hearing loss (nerve deafness) : cause by damage to hair cell receptors or auditory nerves
• most often caused by aging or prolonged exposure to noise
• digital hearing aids can help by amplifing vibrations
• Sensory Compensation: slight enhancement of other sensory abilities after losing one channel
• Synesthesia: joing the senses: sensory crossovers
• error in terms of brain's responsivity
• e.g. hears words, visual cortex activates
• naturally and artifically done

Touch

• Somatosensory perception is essential for maintaining the integrity of the body, for controlling movements, etc
• Phantom sensations demonstrate the hidden but continuous operation of the somatosensory system 
• Phantom Limb Pain
• subjective sensory awareness of an amputated part
• pins-and-needles, burning, shooting pain, cramps
• somatosensory cortex still active in that area
• over 70 % experience intense pain; 80% suffer this
• treatment - 7% success, virtual expensive
• mirror to remaining limb and the perceived movement tricks brain
• cause?
• possibility: Cortical Reorganization of the Somatosensory Cortex

Taste

• Sweet, Salty, Bitter, Sour
• Taste for MSG has also been id'd
• Survival Functions
• sweet = energy source
• salty = sodium essential to physiological processes
• sour = potentially toxic acid
• bitter = potential poisons
• Obesity and evolved processes
• Fittest of ancient = preferred high calorie food, ate to capacity, efficient body-fat storage metabolsim, hunting and killing = high energy
• Current society
• food no longer requires tremendous energy expenditure
• cultural factors contribute to high calorie food central status

Smell

• Process
• Airborne molecules----- receptors at top of your nose
• sniffing swirls air to receptors
• The receptor cells------ brain’s olfactory bulb----- temporal lobe’s primary smell cortex and  parts of the limbic system involved in memory and emotion
• Smell processed near memory area
• smell trigger memory
• Women have superior sense of smell
• theory: help select better mate
• Miniski and Wedekind (2001)
• ovulation (enhanced smell)
• Why'
• segment of DNA, MHC ( major histocompatibility complexe) codes for immune system functioning
• MHC is co-dominant
• tend to select different MHC person
• MHC manifests itself in proteins secreted
• Female rats select with dissimlar MHC mates
• women and cotton t shirt experiment
• MHC dissimilar = mate
• MHC similar = akin to family member
• overly intense disliked
• suggests because strong odors though to indicate disease