MCAT Psychology Ch2 Sensation and Perception

Sensation v. Perception

sensation \= unprocessed AP
perception \= processing sensations

Sensory receptors

respond to stimulus (e.g. light); and can even encode multiple aspects of a stimulus

transduction

conversion of physical stimulus into electrical signals in the CNS

ganglia

cell bodies outside the CNS; sensory neurons may terminate on them.

Threshold

the minimum amount of a stimulus that renders a difference in perception (absolute threshold \= difference in sensation)

Absolute threshold

the minimum stimulus energy that is needed to activate a sensory system; threshold in sensation [candle 30 miles away].

Threshold for conscious perception

a stimulus below the threshold of conscious perception will reach the CNS but will not evoke long/strong enough AP's to

Diference Threshold (jnd)

minimal difference in stimuli before one can perceive a difference.

Webers law

*constant ratio between the change in stimulus magnitude needed to produce a
can't tell the difference between two frequencies unless 0.68 higher or lower different of original frequency

weight \= 0.05 lbs difference

Signal detection theory

perception of stimuli can be influenced by non sensory factors, such as memory, motives, and expectations.

What is a response bias? What would indicate a significant response bias in a signal detection theory test?

tendency to subjects to systematically respond to a stimulus in a particular way *due to non sensory factors*

Catch vs. noise trials

signal detection theory experiment
catch \= sound
noise \= no sound

adaptation

sensory (physiological) and perceptual (psychological) adjustments in detection of a stimulus.

sensory adaptation \= ear muscles contract moving ossicles so we don't hear that much sound

perceptual adaptation \= we do not interpret cold water as "cold" after we are "used to it"

What is the pathway for a stimulus to reach conscious perception?

1. sensory receptor
2. affarent sensory neuron
3. sensory ganglion
4. spinal cord
5. brain

What does adaptation do to the difference threshold?

*Adaptation raises the difference threshold.* Therefore, the difference in stimulus required to evoke a response must be larger

2 muscles that comprise the iris

1. constrictor pupalie --\>SNS
2. dialator pualaie --\> PNS

T/F: The eye has two blood vessels

True: choroidal and retinal

List the layers of the eye from outwards to inwards.

sclera \> choroid \> retina

What produces aqueous humor?

ciliary body

What drains the anterior chamber of the eye?

Canal of Schlemm

What lies in front of the lens?

The iris

Fn. of the ciliary muscle.
What ANS domain is it under?

Fn. --\> to contract, tensing the suspensory ligaments--pulling the lens flat, known as accommodation.

Ciliary muscle is under parasympathetic control
CONTRACT \= near
RELAX \= far

Accommodation

the process of changing lens shape to facilitate visual clarity

T/F: The retina is actually CNS tissue and is derived from brain tissue.

true

Duplexity; Duplicity Theory of Vision

states that the retina contains two kinds of photoreceptors: light and dark detection and color detection

Cones & Cone Naming Conventions

Short \= blue
Medium \= green
Long \= red

What pigment do rods contain?

Rhodopsin

Macula

region of the eye that is darker and absorbs dark blue and violet light (a natural sunblock for the eye)

Fovea

area in the eye with the highest cone concentrations (100% cone), thus, visual acuity is the best here.

Bipolar Cells
Ganglion Cells
Optic Nerve

synapses with rods and cones, terminate on ganglion cells

Why does color vision have greater sensitivity to fine detail than colorless vision?

Because the number of cones represented by a given ganglion cell is less relative to rods, where each ganglion cell represents a larger \# of rods.

Horizontal and Amacrine Cells

cells that receive info from multiple retinal cells in same area before the information is passed onto the ganglion cells--*they are important for edge detection and increase our perception of contrast*

Visual Pathways

AAMC Term:
Refer to both the physical anatomical connections between eye & brain and the flow of visual information along these connections

Draw (or mentally trace) the visual pathway for a duck seen in the left eyes' left visual field.

1. hits the right side of the right eye
2. crosses over at the optic chiasm
3. travels to lateral geniculate nucleus (thalamus)
4. travels to visual cortex
4. part travels to superior colliculus (midbrain)

Septal Nuclei

Part of limbic system. Involved in pleasure and addiction. [Rats that could stimulate their septal nuclei would do so for 24 hours without sleep, etc.]

Superior colliculus

Controls some responses to visual stimuli. When exposed to sudden unexpected sound ... superior colliculus aligns our eye to the sound

Lateral geniculate nucleus

part of thalamus and part of the conduction pathway from retina to brain

Parallel Processing

Ability to analyze color, size, and shape of an object and bring that information together and name an object

Feature Detection

Process by which specialized neurons respond to color shape and motion

*identify desired information (object) in a visual field*

Feature Detection: What cells are responsible for motion?

mango cellular cells detect motion and have very good temporal resolution. However, they have terrible spatial resolution. *(they provide a blurry but moving picture of an object)*

Temporal resolution v spatial resolution

temporal resolution - precision of measurement with respect to time
spatial resolution - precision of measurement with respect to space (fine detail)

Feature Detection:
What neurons detect shape?

parvocellular cells: have high color and spatial resolution but LOW temporal resolution

What is the function of cornea

To gather and focus light. Its focus is fixed though.

Are sound waves longitudinal or traverse?

LONGITUDINAL

pinna

auricle; transmits waves into the external auditory canal;

How do we percieve pitch? Loudness?

Pitch \= frequency of TM vibration
Loudness \= intensity or amplitude of TM vibration

List the ossicles.

1. malleus (hammer)
2. incus (anvil)
3. stapes (stirrup)

What separates outer from middle ear? Middle and inner?

tympanic membrane// meeting of stapes and choclea at the oval window.

Fn of the ossicles

to amplify vibrations from the tympanic membrane to inner ear

Eustachian tube

Helps to equalize pressure between middle ear and external environment.

What 3 structures comprise the inner ear?

1. cochlea
2. vestibule
3. semicircular canals

endolymph vs. perilymph

endolymph is a potassium rich fluid that fills the membranous labyrinth.

perilymph suspends the membranous labyrinth, coushins it, and helps to transmit vibrations.

Mechanism of Cochlea

Split into three scale:

middle scale filled with endolymph:
top \= tectoral membrane
middle \= organ of corti
bttm \= basilar membrane

perilymph movement transmitted to endolymph causes tectoral membrane to move, which causes hair cells to be activated. AP travels to temporal lobe via vestibulochoclear nerve.

What is the function of the round window?

Fluids are incompressible. The round window (membrane covered hole) allows the perilymph in cochlea to move back and forth.

otoliths

resits motion and cause hair cells to fire; found in utricle and saccule

Utricle and Saccule

sensitive to linear motion

Vestibule

contains the utricle and saccula

Semicircular Canals

sensitive to rotational acceleration; arranged perpendicular to each other;

Ampulla

part of semicircular canals where hair cells are; at the base;

Auditory Pathway

1. sound is transmitted from basilar membrane to hair cells in organ of court
2. vestibulochoichular nerve
3. spinal cord
4. medial geniculate nucleus
5. auditory cortex in temporal lobe
5. inferior colliculus (vestibulo-ocular reflex)(startle reflex)
5. superior olive (localizes sound)

stereocillia

hair cells hair; hair cells on the tectoral membrane are responsible for amplifying incoming sound

How can the brain gauge pitch?

because the cochlea is tonotopically organized \-- the basilar membrane changes it thickness depending on its location in the chochela \-- high pitch vibrations cause basilar membrane vibration close to oval window while low frequency vibrations cause basilar membrane vibration towards the apex (away from oval window).

T/F: Smell is the only sense that does not travel through the thalamus first

TRUE

List the steps in the olfactory pathway.

1. volatile chemical binds olfactory chemoreceptors in olfactory epithelium
2. activated olfactory chemoreceptors send signal to olfactory bulb
3. olfactory tract relays these signals to higher order brain centers (including limbic system)

List the steps in the taste pathway.

1. chemicals bind taste receptors at papillae
2. taste buds to brainstem which *ascends to the taste center in thalamus*
3. higher order brain regions

4 modalities of somatosensation

1. pressure
2. vibration
3. pain
4. temperature

What are the 5 receptor classes involved in somosensation.

1. pancian corpsules --\> deep pressure & vibes
2. ruffini endings --\> stretch
3. Messier corpules --\> light touch
4. Merkle Discs -\> deep pressure & texture
5. Free nerve endings --\> pain and temp

Pancinian Corpsucles

Deep pressure & vibration

Rufinni Endings

Stretch

Messier Corpsules

light touch

Merkle Discs

Deep pressure & texture

Free Nerve Endings

Pain and temp

What is the somatosensation pathway.

1. receptor (Merkels Dics, Rufinni End, Panician Corpsulce, Messinger, free endings)
2. spinal cord (spinal nerve)
3. somatosensory cortex (parietal lobe)

Cranial vs. spinal nerves

cranial \-- away from brain
spinal \-- towards brain

Two pt. threshold

*Touch perception*
minimum distance that skin stimulation will be felt as two distinct stimuli \-- depends on nerve density

small two point threshold means lots of density

physiological zero

*touch perception*
normal temperature of the skin (37C) (between 86 and 97 F)

Gate Theory of Pain

*touch perception*
spinal cord is able to preferentially forward the signals from other touch modalities (pressure, temperature) to the brain, reducing pain sensation

this is why rubbing an injury may make it feel less painful

Kinesthetic sense

*proprioception*
ability to tell where one's body is in space;

receptors for proprioception are mainly found in muscles and joints.

top-down vs. bottom-up processing

*top-down: (conceptually driven)*
starts with the whole image and through memory creates expectations for the objects components (Dalmatian)

*bottom-up: (data-driven)*
each component must be interpreted using parallel processing and feature detection to take sensory stimuli and combine it together to make a cohesive image before determining what an object is.

Perceptual organization

Perceptual organization is a process that forms a complete picture by applying all the sensory ideas about an object through top-down and bottom-up processing: depth, form, motion, constancy. Using gestalt principals, we can fill in the gaps

Gestalt principles

ways we can infer missing parts of a picture using certain principals

Law of proximity

Gestalt principal:
elements close together are perceived as a unit

Law of similarity

objects that are similar tend to be grouped together

Law of good continuation

elements that appear to follow in the same pathway tend to be grouped together

subjective contours

perceiving contours and shapes that are not actually present in the stimulus

Law of closure

says that when a space is enclosed by a contour, it tends to be perceived as a complete figure.

Law of pragnanz

perceptual organization will always be as regular, simple, and symmetric as possible.

Signal vs. feature detection

*signal detection* - changes in our perception of a sensory factor based on non-sensory psychological factors: like internal personality and the social environment

*feature detection* - using color, shape, motion: ability to combine and analyze info about color shape motion; [VISION]

T/F: Rods have mitochondria, nucleus, and 1 rhodopson pigment

Differentiate between temporal vs. nasal fibers

nasal fibers cross at chiasm:
temporal outside neurons nasal inside neurons

Iris contracts, what happens to pupil?

enlarges

Compare vestibule with semi circular canals and cochlea

chochlea \= hearing
vestibule \= linear motion
ss canals \= rotational acceleration

Order of AP from auditory nerve

1. auditory nerve
2. superior olive
3. inferior collicucls
4. medial geniculate nucleus
5. auditory cortex of temporal lobe

What waveform does sound assume? vision?

sound \= longitudinal
light \= transverse

T/F: vestibular sense requires a chemical receptor

FALSE: vestibular sense does not involve a chemical receptor

Instinctive drift

inability to train an animal to overcome a behavior because they have a natural pre disposition to that behavior (raccoons putting coins in a piggy bank)

3 R's of retrieval

Relearning --\> previously stored information is relearned quickly

Recall --\> statement of previously learned info (50 ppl from HS graduating class)

Recognition --\> identify a previously learned item with a little help (50 ppl from HS graduating class with pic)