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 SystemsInformation is acquired and then TRANSDUCED

ThresholdsABSOLUTE 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 CodingFirst 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 lightCones 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 VisionColor is the result of differing light wavelengths (except…)

Color mixing (red, blue, green) can create any hueSuggests 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 EarEardrum – membrane that vibrates

Malleus, Incus, Stapes – bones that vibrate the next membrane (oval window)

Inner EarCochlea – coiled bone that contains the auditory receptors, filled with fluid

Basilar Membrane – section of cochlea that contain “hair cells”

Hearing LossConduction loss

Poor conduction in the middle ear – requires greater frequencies

Sensory-neural lossInner ear damage (hair cells are unable to regenerate)

Hearing PitchTemporal Theory

Frequency of stimulus creates vibration of the entire basilar membrane which causes us to hear a specific pitch.

Place TheoryEach place along the basilar membrane corresponds to a pitch sensation.

OlfactionAnimals 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

GustationExperience 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)

PainPhasic 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

PerceptionModel 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

AttentionWe 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

LocalizationFigure and Ground – visualize stimulus in these two regions

Grouping – we see patterns as going together

Distance Perception

Binocular Cues – using both eyesBinocular Disparity – difference in the views seen by each eye

Monocular Cues – using a single eyeRelative Size

Interposition

Relative Height

Perspective

Shading

Motion

Stroboscopic vs. Real Motion

Images appear on different parts of our retina simultaneously

An image moves across our retina

RecognitionRole 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 inputProsopagnosia – 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 IllusionMoon 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 roomSize 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 studiesPreferential 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