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School: Florida International University
Department: Psychology
Course: Sensation and Perception
Professor: Timothy allen
Term: Spring 2016
Cost: 50
Name: Sensation and Perception Exam 1 review
Description: Intro to sensation and perception visual system
Uploaded: 02/08/2016
12 Pages 12 Views 7 Unlocks

Sensation and Perception

The basis of perception.

∙ Dualism: The idea of mind and body  

∙ “I think, therefore I am”

∙ Monism: Mind is a manifest property of the physical matter of the brain

∙ Empiricism: Socially facilitated (Experience of the senses,  observation, scientific method)  

∙ Top-down process: using your knowledge (memory, emotional  state, beliefs, concepts, expectations) to interpret sensory  information

∙ Ex: Cedar/orange experiment

∙ Bottom-down processes: Building percepts from elemental  senses, influence from a neural base

The Myth of five senses

∙ 7-12 different sensory systems

∙ Sensory systems often interact (multisensory processing) ∙ One sense can affect the perception of another

The basis of perception

∙ Sensation: The registration of physical stimuli on sensory  receptors.  

∙ Perception: The process of creating conscious perceptual  experience from sensory input. Perception occurs after cognitive  processing begins.  

Reasearch Methodology

∙ Transduction: The process of converting a physical stimulus into  an electrochemical signal

∙ Neural Response: he signal produced by receptor cells that can  then be sent to the brain

∙ Sensation refers to the process of transduction in which  receptors convert physical signals into neural responses and  perception refers to the process of taking that signal and  processing it into a usable image or experience.  

∙ Ex: at an orchestra: sensation takes in sounds, perception  appreciates music.  

The beginnings

∙ Aristotle conducted conceptual work and observations ∙ Gave us our basic list of the five senses

∙ The Aristotle illusion

∙ Aftereffect: a sensory experience that occurs after prolonged  experience of visual motion in one particular direction 19th century:  

Johannes Mueller

∙ The doctrine of specific nerve energies: the argument that it is the specific neurons activated that determine the particular  type of experience

Whats is unconcious interference?

Don't forget about the age old question of taliyah guide

∙ What determines hearing, sight, etc.  

∙ It matters what receptors are activated, not how they are  activated

∙ Percept is based on what those receptors do

∙ Our entire consciousness is based on the activity of our  neurons


∙ Had a constructivist approach  

∙ (the idea that perceptions are constructed using information  from our senses and our cognitive processes)  

∙ Held the belief that we must incorporate information from our  existing knowledge to completely perceive the world around  us.  Don't forget about the age old question of ∙ CD4 cells – decreasing/death – virus is attacking and killing them ∙ Why is the virus increasing over time and the immune system is not destroying the virus?

∙ Unconscious interference: perception is not adequately  determined by sensory information, so an interference or an  educated guess is part of the process this interference is not  the result of active problem solving but rather a non conscious cognitive process

Hering 

∙ Opposed Helmholtz

∙ Viewed environmental inputs and senses enough to perceive  world


∙ Weber’s law: a just noticeable difference between two  stimuli is related to the magnitude or strength of the  



∙ Father of psychophysics

∙ Psychophysics: the study of the relation between physical  stimuli and perceptual events

∙ Goal was to describe sensation/perception in mathematical terms


∙ Magnitude estimation

20th century

Gestalt psychology

∙ Viewed the world in terms of general patterns and well organized structures

∙ Interested in how edges are perceived

∙ Believed perceptual laws and other principles of human  behavior were genetically wired Don't forget about the age old question of ssc 101

∙ German origins

∙ You cannot understand perception without organization ∙ Law of common fate: we can only interpret sensory info in  holistic ways or concepts. Objects with common motion  (fate) are grouped together

Direct perception (The Gibsonian Approach)

∙ Directly opposes concept of unconscious interference ∙ World generates rich sources of info that senses need to  merely pick up on

∙ Ecological realism

Information processing approach

∙ Info is collected by sensory processes and then flows to a  variety of modules that decode info, interpret, and allow  organism to act on it.  

∙ Brain is parallel: many processes can be occurring  simultaneously

∙ More like Helmholtz’s view

∙ Info processing allows for interpretation vs. direct  

processing which says that sensory info is sufficient  


21st century

Neuroscience Approach

∙ Able to measure and manipulate nervous system directly Computational approach

∙ Influenced by computer science

∙ Marr sought mathematical explanation for perceptual  processes

∙ Models perception in nonhuman systems

Sensation and Perception

 Research Methodology:  We also discuss several other topics like What happens in the brain?

∙ Psychophysical scale: a scale which people rate their  psychological experience as a function of the level of a physical  stimulus

Ex: Scoville scale- measures our detection of the amount  of an ingredient called capsaicin in chili peppers

∙ The study of human sensory systems starts with psychophysics.   The Measures and Methods of Psychophysics

∙ Method of limits: stimuli are presented in a graduated scale, and  participants must judge the stimuli along a certain property that  goes up or down

o Ex: A participant may be presented with an increasingly  dimmer set of lights. The participant is asked to tell when  the lights are no longer visible

o Is used to determine absolute and difference thresholds o To determine absolute threshold with method of limits  ascending (stimulus gets larger along a physical  

dimension) and descending (stimulus gets smaller) series  is used.  

o Crossover point

o Two point threshold (an absolute threshold)  

∙ Method of Constant stimuli: A method whereby the threshold is  determined by presenting the observer with a set of stimuli,  some above threshold and some below it, in a random order o Stimuli is given in a random order We also discuss several other topics like soc 104 ku

o Prevents observer from being able to predict the next  stimulus

o Reduced errors due to habitation  

o Time-consuming

o Requires many trials

∙ Method of Adjustment: method whereby the observer controls  the level of stimulus and "adjusts" it to be at the perceptual  threshold Don't forget about the age old question of Who invented and used the early microscope to discover the cell?

o Mirrors normal activities; i.e. adjusting volume control o Quickly yields thresholds (advantage)  

o Great variance from one participant to the next  


o Useful for determining PSE

∙ Magnitude Estimation: a psychophysical method in which  participants judge and assign numerical estimates to the  perceived strength of a stimulus

∙ “P” = perceived magnitude

∙ “c” = scaling constant

∙ “I” = stimulus intensity

∙ “b” = exponent constant (raised power)

o Response compression ( b < 1) sight, hearing, touch etc.  o Response expansion ( b > 1) pain  

o Stevens’ power law

 ∙     Catch Trials 

o Participant may be willingly or unwillingly misinforming the  experimenter about perceptual experience

o Catch trials counter this, and limits false reporting o Forced choice method

∙ Signal detection theory: the theory that in every sensory  detection or discrimination, there is both sensory sensitivity to  the stimulus and a criterion used to make a cognitive decision

o Sensitivity (the ease or difficulty with which an observer  can distinguish signal from noise)

o As sensitivity decreases, more false alarms and misses  occur. As sensitivity increases, the observer has more hits  and correct rejections

o d’ (d-prime)  

o Relationship between sensitivity and criterion  

o ROC curve simplifies all possible outcomes


∙ Vision is the system that allows us to perceive light ∙ Visible light is an example of electromagnetic energy  ∙ Light is made up of particles called photons that behave in a  wave-like manner

∙ The shorter the wavelength the higher the energy. The longer the wavelength, the lower the energy

∙ *Red has a wavelength approaching 700 nm (the longest  wavelengths we can perceive)  

∙ Term photon is used when discussing brightness and intensity.  The term wavelength is used when discussing color

The Eye

∙ Our eyes are located in the front and slightly spaced which gives  us good depth perception  

∙ Reflected light enters eye through the pupil and is focused on the retina by the cornea and the lens. The retina contains specialized cells called rods and cones which transduce light energy into an  electrochemical signal which is then sent to the brain for  processing through the optic nerve.  

Field of view

∙ Part of the world you can see without eye movements.  Approximately 190 degrees horizontally and 140 degrees  vertically


∙ Clear front surface of the eye that allows light in  

∙ Major focusing element of the eye

∙ Begins process of refracting light to come into focus on the  retina of the eye

∙ Is transparent  

∙ Cornea is rigid therefore changes in refraction come from the  adjustable lens

Sclera: Tough membrane which provides protective covering for  the eye

Anterior chamber: fluid-filled space between the cornea and  the iris

Iris: colored part of the eye, muscle that controls the amount of  light entering through the pupil

Pupil: an opening in the middle of the iris

∙ Light enters through the opening

∙ Pupil expands (dilates) in dim light (iris relaxes control)

∙ Pupil narrows in bright light (iris contracts)

∙ Process not directly under conscious control…known as  pupillary reflex

∙ Pupil can range from 2mm to 8mm in diameter

Posterior chamber: space between the iris and the lens which  is filled with aqueous humor fluid.  

 The lens

∙ Ciliary muscles: muscles connected to the lens through which  accommodation is controlled. Can contract and increase  

curvature of lens

∙ Zonule fibers: the ciliary muscles work together with these fibers  and connects lens to choroid membrane

∙ When looking far, lens relaxes which allows us to look at a  distant object

∙ When looking near, lens contracts which allows you to focus  The Retina

∙ The retina is the eye’s photosensitive surface

∙ Goal of other parts of the eye is to focus an image on the retina ∙ The retina is thin and composed of several interconnected layers ∙ The retina is in the location where transduction takes place ∙ Starts the process of transmitting visual information to the brain   The receptors: rods and cones



∙ At the periphery of retina ∙ Very light sensitive

∙ Specialized for night vision ∙ 120 million in each eye

∙ Only one type

∙ Sees only in shades of gray  (black to white)

∙ No rods in fovea

∙ Photopigment: rhodopsin ∙ Scotopic system

∙ Clustered at the fovea  


∙ High visual acuity

∙ Responsible for color vision ∙ 7 million in each eye

∙ Three classes of cones

∙ Photopigment:  


∙ Photopic system

 Transduction of light  

∙ Rods and cones are equipped with the ability to convert light into a neural signal by using photopigments. 

∙ Photopigments absorb light and release an electric potential ∙ When it absorbs light, it changes shape

∙ Change in shape initiates series of biochemical processes

∙ Nature of photopigment is central to determining how the  receptor behaves with regard to light

∙ Absorption of photon by photopigment causes receptor to have  more negative voltage inside relative to outside the receptor  known as hyperpolarization 

∙ Hyperpolarization causes receptor to release less of the  neurotransmitter

∙ Light is inhibitory

∙ Light inhibits release of inhibitory neurotransmitter which in turn  excites visual system

 The Duplex Theory of Vision  

∙ There are functionally two distinct ways in which our eyes work ∙ However there is a range of intermediate ambient light intensity  within both systems work (mesopic vision)  

Scotopic system

Photopic system

∙ Vision associated with rods ∙ More sensitive to different  and shorter wavelengths  

(spectral sensitivity)

∙ Sensitive to under 500 nm ∙ Convergence: is the pooling  of information happens  

greater for rods than for  


∙ Many rods connect to one  retinal ganglion cell

∙ Vision associated with cones ∙ More sensitive to longer  wavelengths

∙ Sensitive to about 555 nm ∙ Difference in sensitivity is  known as purkinje shift

∙ One cone usually connects  to one ganglion cell which  

maximizes the ability to  

pinpoint the source of light  

in space

∙ Limits spacial confusion

 Retinal ganglion cells and receptive fields

∙ Only about 1.1 million ganglion cells

∙ Most ganglion cells receive inputs from many different  


∙ Forming of receptive fields (array of photoreceptors from which  each retinal ganglion cell receives input)  

∙ As you move away from the fovea, ganglion receptive fields get  progressively larger which allows greater convergence and  greater sensitivity to dim light

∙ Ganglion cells start the process of edge detection 

∙ Earliest stage of edge detection occurs in the retinal ganglion  cells known as center-surround receptive fields.  

 Lateral inhibition: goal is to facilitate edge detection

∙ Horseshoe crab

∙ Herman grid

Visual System: The brain

The Optic nerve and chiasm

∙ The optic nerve of the left eye and the optic nerve of the right  eye meet just a couple centimeters behind the eyes in an area  called the optic chiasm 

∙ The optic nerve from each eye splits in half at the optic chiasm ∙ Axons from the right half of the right retina and the ganglion cells from the right half of the left retina combine which forms the  optic tract

∙ Contralateral representation of visual space occurs: this is  opposite side organization in the visual system, the nasal  

retina projects to the opposite side of the brain

∙ Information from each eye goes to both hemispheres  

(ipsilateral organization) 

∙ Once optic tract has left chiasm, 90% of axons make their way to LGN of the thalamus

∙ 10 % go to other locations

The Lateral Geniculate Nucleus

∙ LGN is bilateral structure in thalamus that relays information  from optic nerve to visual cortex

∙ Critical locus for vision

∙ Has 6 layers

∙ LGN preserves info specific to eye and visual field

∙ This is important for us to construct a 3-d image




∙ Layer 1 : receives info from  

contralateral eye

∙ Layer 2: receive  

info from  

ipsilateral eye

∙ Parasol retinal  

ganglion cells (M  


∙ M cells have large  receptive field  

and are sensitive  

to light but not  


∙ Light detection  

and motion  


∙ Layer 3:  


∙ Layer 4:  


∙ Layer 5:  


∙ Layer 6:  


∙ Midget retinal  

ganglion cells (P


∙ P cells receive  

info from single  

cone, contains  

detailed info  

necessary for  

visual acuity

∙ Sensitive to  

wavelength and  

other foveal  


∙ There are 6 (one  

under each of the  

magno and  

parvocellular layers)

∙ Bistratified ganglion  cells

∙ K cells have more  

convergence, lower  


The Superior Colliculus:  

∙ Main function is the control of rapid eye movements

∙ 10% of retinal ganglion cells synapse

∙ smooth pursuits: voluntary tracking eye movements Ex:  watching a bird fly across the sky

∙ Saccades: sudden eye movements used to look at one object  from another

∙ Is an organ of multisensory integration  

The Primary Visual Cortex:  

∙ V1 (Has retinotopic map of the retina)

∙ Fovea has larger cortical area than the periphery  

∙ Also has 6 layers

∙ Layer 4 is critical layer that receives input from LGN  Receptive fields of V1 cells

∙ Simple cells: neurons that respond to stimuli with particular  orientations to objects within their receptive fields.

∙ Like cells in LGN they have clear excitatory and inhibitory  regions

∙ Unlike LGN cells they have orientation selectivity rather than  center-surround visual fields

∙ V1 indicates the orientation of lines in the visual world by  having select cells respond to different angles of orientation   Complex cells  

∙ Neurons in V1 that respond optimally to stimuli with particular  orientations

∙ Unlike simple cells they respond to a variety of stimuli across  different locations.  

∙ Complex cells do not have a peak location sensitivity like simple  cells do.  

∙ Complex cells are found in layers 2, 3, 5, and 6 of V1 but not  layer 4.  

∙ End-stopped neurons: neurons respond to stimuli that end within  the cell’s receptive field.  

∙ Blobs are areas within V1 sensitive to color

∙ Interblobs: areas sensitive to the orientation of an object ∙ Layer 4B cells


∙ After information leaves V1 it travels to other areas in the  occipital cortex such as V2

∙ There are 3 distinct regions within V2 which match directly with 3 different types of cells in V1

∙ Blobs connect to thin stripes

∙ Layer 4B connects to thick stripes

∙ Interblobs connect to interstripes

∙ Seems to be involved in representation

Functional Pathways in the Visual Cortex:  ∙ Ventral pathway (P pathway) “what” ∙ Dorsal pathway (M pathway “where”

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