Class Notes (809,509)
Canada (493,754)
Psychology (6,041)

Textbook Notes.docx

24 Pages
Unlock Document

Western University
Psychology 2015A/B
Patrick Brown

Psychology 2015: Sensation & Perception Chapter 1: Introduction to Perception (Pg. 3) - The detectors include the eyes, ears, skin receptors, and receptors in the nose and mouth - Perceiving occurs almost effortlessly The Perceptual Process - The Perceptual Process- A sequence of processes that work together to determine our experience of and reaction to stimuli in the environment - Process is divided into 4 categories: o Stimulus- What is out there in the environment, what we actually pay attention to, what stimulates our receptors  The stimulus can be in environment or within a person’s body  Environmental stimuli- All things in our environment that we can potentially perceive  Attended stimuli- Things that are particularly focused on by the observer; Changes from moment to moment  The attended stimulus is transformed into an image on the retina  Image is representation of stimulus  The next step involves transforming the image into electricity o Electricity- Electrical signals created by the receptors, which turn energy from environment into electrical signals in the nervous system  Everything we perceive is based on electrical signals in our nervous system  Transduction- Transformation of one form of energy into another occurs in the nervous system when energy (light energy, mechanical pressure, chemical energy) is transformed into electrical energy  Transmission- Once the image is transformed into electrical energy signals (through transduction), those signals travel from neuron to neuron until they reach the brain  Processing- Neural processing involves interactions between neurons, relaying the representation of the stimulus from the eye to the brain  As electrical signals are transmitted, they undergo neural processing  The original electrical representation created by the receptors is transformed by processing into a new representation of the stimulus in the brain o Experience & Action- Our goal is to perceive, recognize, and react to the stimuli  Perception- Conscious sensory experience occurring when electrical signals representing the stimulus are transformed into an experience of observing the stimulus  Recognition- Our ability to place an object in a category that gives it meaning  Visual Form Agnosia- An inability to recognize objects even after perceiving the object  Action- Motor activities that occur as a result of or following perception  In evolution, major goal of visual processing was to help animals control navigation; Functions for animals survival  Perception is a continuously changing process  Overall process is so dynamic and continually changing that is doesn’t really have a beginning or ending point  Everyone can see an action but experience is personal  Experience probably leads to action  Subjective experience can’t be measured o Knowledge- Any information we bring to the perceptual situation— Can have its effects at many different points in the process  Knowledge allows for the categorization of objects  Rat-Man Demonstration- Picture that looks like a rat and a man; Shows how recently acquired knowledge can influence perception  Bottom-Up Processing (Data-Based Processes)- Processing based on incoming data  Essential for perception b/c perceptual process begins with stimulation of receptors  Top-Down Processing (Knowledge-Based Processing- Processing based on previously acquired knowledge  Both types of processing often work together to create perception  For simple stimuli, bottom-up processing can occur on its own  When stimuli become more complex, top-down processing increases  Our knowledge of how things usually appear in environment can help determine what we perceive - Retina- 0.4mm thick network of light-sensitive receptors and other neurons that line the back of the eye that transforms stimuli into images/representations o Representation of attended stimuli is created on the retina o Light energy from the representation/image is transformed into electrical energy How to Approach the Study of Perception - Goal of perceptual research is to understand steps in process that lead to perception - Studied using 2 approaches: Psychophysical approach & physiological approach - Psychophysical Approach- Measuring the stimulus-perception relationship. Gustav Fechner coined the term psychophysics Referring to the measure of relationships between stimuli and perception - Physiological Approach- Measuring the relationship between stimulus and physiological processes, and physiological processes and perception o Studied by measuring electrical responses; Can also involve studying anatomy or chemical processes o Goal is to understand how neurons and the brain create perceptions - Cognitive Influences on Perception- Knowledge, past experiences, expectations, memories, and expectations that people bring to the situations that affect how we perceive things - To fully understand perception we need to use both approaches Measuring Perception - Many possible perceptual responses to a stimulus: - Description- Indicating characteristics of a stimulus o Phenomenological Method- Researcher asks to describe what we perceive or to say when a particular perception occurs  First step in studying perception because it describes what we perceive - Recognition- Placing the stimulus in a specific category o When categorizing a stimulus by naming it, we are measuring recognition - Detection- Becoming aware of a barely detectable aspect of a stimulus o Classical Psychophysical Methods- The original methods used to measure stimulus-perception relationship; Methods of limits, adjustment and constant stimuli used to measure stimulus-perception relationship  Method of Limits- Experimenter presents stimuli in ascending (increasing intensity) or descending (decreasing intensity) order until the person can perceive the stimulus or can’t perceive the stimulus anymore  The change is called the crossover point  By repeating many times, starting above threshold half the time and below the other half, experimenter can determine threshold by getting average of all crossover points  Method of Adjustment- Experimenter adjusts the stimulus intensity continuously until the observer can just barely detect the stimulus (fastest method)  The just barely audible intensity is the absolute threshold; Can repeat many times and get average  Method of Constant Stimuli-Experimenter presents 5-9 stimuli with different intensities in random orders (most accurate but time consuming)  Threshold determined by intensity that results in detection on 50% of trials o Absolute Threshold- The smallest amount of stimulus energy necessary to detect a stimulus o Difference Threshold (DL)- The smallest difference between two stimuli a person can detect  Fechner’s methods can be used but participants are asked whether they detect a difference between 2 stimuli  Difference threshold is measured difference between standard and comparison stimuli when observer says there is a difference  Weber’s Law- The ratio of the DL to the standard stimulus is constant such that K= DL/S  As the magnitude of the stimulus increases, so does the DL  Ratio of DL to standard stimulus is constant  Weber Fraction- The proportion by which a standard stimulus must be changed in order for the change to be detected; The ratio of DL to the weight of the standard; “K” is stands for a constant  “S” is the value of the standard stimulus  Weber’s law is true for most senses as long as stimulus intensity isn’t too close to threshold  Each sensory judgment has its own Weber fraction - Magnitude Estimation/Scaling- Measuring the above-threshold perceptions, being aware of their intensities/sizes o Experimenter gives number value to standard stimulus and observer gives value to stimulus by comparing to standard  Standard may not be used and observer just gives number value to each stimuli o Most experiences consist of perceptions far above threshold o Response Compression- As intensity increases, the magnitude increases as well BUT not as rapidly as the intensity  Doubling intensity doesn’t always double perceived intensity o Response Expansion- As intensity is increased, perceptual magnitude increases more than intensity o Power Functions- The functions of the relationship between perceived intensity of a stimulus and perception of its magnitude, which follow same equation for each sense P=KS^n o Stevens’ Power Law- The relationship between perceived intensity of a stimulus and perception of its magnitude Perceived magnitude (P) equals a constant (K) times the stimulus intensity (S) raised to a power (n) Search - Looking for specific stimulus among a number of other stimuli o Visual Search- Observer’s task is to find one stimulus among many as quickly as possible o Reaction Time- Time between presentation of a stimulus and the observer’s response to the stimulus - Response Criterion- Observer’s tendency to respond yes or no (response criterion is high when a person says yes only when they are sure) o Only necessary to take into account when comparing 2 people’s responses Class Notes: Why Study Perception? - Medical Applications- Devices to assist people with vision and hearing loss - The visual system: o Retina Sub-Cortical Structures Primary Visual Cortex (at back of brain) Temporal Lobe (on each side of brain) - Representation of image on retina is patterns of light and dark, no colour o At each stage of processing, the representation is refined - The tasks the visual system carries out to generate your visual experience of the world: o Light and dark Organized light and dark Features (e.g., edges) Objects - Things can go wrong with transduction, transmission, and processing and cause different forms of visual impairment - Perception occurs as conscious perception - Experience means subjective experience - Perception is determined by interaction with botton-up and top-down processing - Psychophysical Approach (PP)- The stimulus-perception relationship - Physiological Approach (PH1)- The stimulus-physiology relationship - Physiological Approach (PH2)- The physiology-perception relationship Class Notes: Psychophysics - The basic task of a sensory system is to detect energy changes in the environment - Most animals detect energy in multiple modalities o Modality- A system that responds to energy of a particular kind - Threshold Stimuli- Stimuli just above or below the threshold of energy needed for you to perceive a signal - We no longer believe there’s an absolute threshold o Turns out absolute threshold isn’t a fixed value but changes from series to series - Staircase Method- Revised method of limits; The experimenter changes the direction each time the observer changes his/her response o Allows experimenter to track threshold if it changes - Adaption- Occurs if sensory receptors change their sensitivity to a stimulus o Dark- and light-adaption o Affects change in threshold - Exogenous- Generated outside the nervous system o E.g., outside noise o Affects change in threshold - Endogenous- Generated inside the nervous system o Random nerve firings o Affects change in threshold - Response Bias- How an observer want to present themselves or how they are going to be strategic affects their response on a trial - Identification- When the stimulus is clearly above threshold and the questions is asking what the stimulus is o Difficulty of task depends on the number of things the stimulus might be o Information Theory- States that an observers identification of a stimulus depends on the nature of both the channel and the signal  Channel- The observer through which information is transmitted  Signal- The stimulus in the environment; We describe signal in terms of how complex it is o We quantify information in terms of how many questions we must ask to discover the identity of the stimulus  E.g., if there are only two alternatives you only need to ask one question to figure it out (e.g., when flipping a coin heads or tails?)  Each question eliminates half the alternatives and defines “1 bit” of information  The amount of information in a stimulus depends on the number of possible stimuli o Discrimination questions ask if one stimulus is different from another and want to find out the just noticeable difference (JND) o Just Noticeable Difference (JND)- The difference in comparison that is noticed half of the time - Scaling- A rule by which we assign numbers to objects or events; Different types of scales  Nominal- Means names; Assign names to things as a way of organizing things  Ordinal- A ranking scale (rank order); The order doesn’t show the difference between intervals  Interval- Get information about the differences between 2 intervals; Doesn’t have true zeros (0 degrees outside doesn’t mean there’s no temperature)  Ratio- Same as interval has true zeros (zero money in wallet=no money)  Indirect Scaling- Assuming Weber’s law is true and then assumed that every JND on a given dimension is the same as any other on that dimension  Fetchner’s Law- S=W logl; For weak stimuli the intensity of sensation grows rapidly with increasing stimulus intensity but then the rate of increase slows down  Direct Scaling- Asks people difference in magnitude of two stimuli with a particular value  Magnitude Estimation- Observer is shown a standard stimulus and told it has a particular value (e.g., 10); Then they assign numbers to new stimuli  With this is was found that sensation was a power function of stimuli intensity: S=al^n Appendix: Signal Detection Theory (Pg. 401) - Signal detection experiments differ from psychophysical experiments b/c… o Only one stimulus intensity is presented o On some of the trials, no stimulus is presented at all - Hit- Correctly saying “yes” when a stimulus is present - Miss- Incorrectly saying “no” when a stimulus is actually present - False Alarm- Incorrectly saying “yes” when no stimulus is present - Correct Rejection- Correctly saying “no” when there is no stimulus present - Payoffs- Means of manipulating each person’s response patterns by changing their response criterion (i.e. giving them incentives for correct hits and correct rejections and/or punishments for misses and false alarms) - Receiver Operating Characteristic (ROC) Curve- Person’s sensitivity to stimuli intensities is indicated by the ROC curve - In the signal detection theory, a person’s sensitivity is indicated by the shape of the ROC curve Signal and Noise - Signal- Stimulus that is presented to the person (i.e. tone) - Noise- All the other stimuli in the environment— Can sometimes be mistaken for the stimulus itself and thus cause false alarms - Signal detection theory looks at experiments not as stimulus present VS stimulus not present BUT as stimulus + noise (S+N) VS just noise (N) Probability Distributions - The perceptual effect “loudness” is what the person experiences in each trial - In SDT experiments, the stimuli intensity stays the same (if present) and the change in perceived loudness is due to changes in person’s attention or changes to state of person’s auditory system - Different likelihoods of a stimulus being present as a result of the observer’s perceived loudness of the tone (stimulus) At a low level of perceived loudness there is a strong likelihood that it is due to noise and as the perceived loudness increases the probability of it being a signal + noise trial increases - At a perceived loudness where it is equally as likely to be N or S + N (where the curves overlap), the person’s decision depends on the location of his criterion - SEE GRAPH ON PAGE 404 The Criterion - According to SDT, once a person has a criterion they use the following rule to decide how to respond to different trials: If perceptual effect (loudness) is greater than (to the right of) the criterion they say “yes, stimuli was present” and if below they say “no, wasn’t present” - Three different criterion: o Liberal (L)— High likelihood to say “yes” to (N) and (S+N), therefore high probability for false alarms for (N) AND hits for (S+N) o Neutral (N)— Low likelihood of saying “yes” for (N) but high for (S+N), low probability for false alarms for (N) BUT high probability for hits for (S+N) o Conservative (C)— High likelihood to say “no” even to (N) and (S+N), therefore low probability for false alarms for (N) AND hits for (S+N) - Distance- A person’s sensitivity to a stimulus is indicated by the distance (d’) between the peaks of the N and S + N distributions and this distance affects the shape of the ROC curve o High sensitivity indicated by large d’ between the N and S + N distributions o High sensitivity creates a ROC curve that is more bowed increasing the d’ between N and S + N probability distributions changes the shape of the ROC curve Chapter 3: Introduction to Vision (Pg. 43) Focusing Light onto the Retina - Vision occurs when visible light is reflected from objects into the eye - Electromagnetic Spectrum- Continuum of electromagnetic energy produced by electric charges and radiated as waves o Energy can be described by its wavelength o Wavelength- Distance between the peaks of the electromagnetic waves; Length of one cycle, from any point on a wave to that same point again  Ranges from short-wavelength gamma rays to long-wavelength radio waves o Visible Light- The energy within the spectrum perceivable to humans contains wavelengths ranging from 400-700 nanometers (nm) - The Eye- Where vision begins o Pupil- Light reflected from objects in the environment enters through the pupil o Cornea- Focus the light that entered through the pupil and form images on the retina, accounts for 80% of the eye’s focusing power BUT cannot adjust its focus o Lens- Focus the light that entered through the pupil and form images on the retina, supplies the remaining 20% of focusing power and changes its shape to adjust the eye’s focus for stimuli at different distances o Retina- Contains the 2 receptors for vision o Rods & Cones- The 2 types of visual receptors, which contain visual pigments o Visual Pigments- Light-sensitive chemicals that react to light and trigger electrical signals  Signals flow through network of neurons that make up the retina  Signals emerge from back of eye to optic nerve o Optic Nerve- Conducts signals toward the brain o Accommodation- Allows for the adjustment of lens to focus stimuli at different distances  The ciliary muscles at front of eye tighten and increase curvature of the lens so it gets thicker  If object is over 20ft away, the light rays that reach eye are parallel but are brought to focus on retina  If object moves closer, the reflected light rays enter eye at more of an angle and lens must accommodate to focus image on retina (instead of behind retina)  Near Point- Distance at which your lens can no longer adjust to bring close objects into focus  Presbyopia- A condition that causes the distance of near point to increase with age because the lens hardens and ciliary muscles get weaker o At age 45, ability to accommodate decreases rapidly; 2 solutions are hold objects further or wear glasses  Myopia/Nearsightedness- Inability to see distant objects clearly; Eye Brings parallel rays of light into focus in front of retina o Can be caused by: Refractive Myopia (cornea/lens bends light too much) OR Axial Myopia (eyeball is too long as a result of thinning of the sclera (wall of the eye)) o Solutions include: Glasses (bend light so it’s focused as if it were at far point) or surgical procedures (lasers are used to change shape of cornes  Far Point- Distance at which the spot of light becomes focused on the retina  Hyperopia/Farsightedness- Can see distant objects clearly but trouble seeing nearby objects; Focus point of parallel light rays is behind retina o Usually because eyeball is too short o The constant need to accommodate when looking at close objects can cause eyestrain and headaches  Laser-Assisted in Situ Keratomileusis (LASIK)- Surgical procedure to correct vision; Uses type of laser called excimer laser Transforming Light into Electricity - Rods: o Outer Segment- Key part of the rod for transduction b/c it is here that lights acts to create electricity  Visual Pigment Molecules- Outer segment contains discs with thousands of these molecules  Opsin- Long strand of protein looping 7 times across disc membrane; A large protein  Retinal- Each visual pigment molecule contains only one of these, part that is sensitive to light therefore crucial to transduction; A light sensitive molecule o Isomerization- When a photon of light hits the retinal and changes its shape so it sticks our from the opsin  Triggers transduction - Hecht’s Psychophysical Experiment- Psychophysical experiment to conclude how many visual pigment molecules need to be isomerized for person to see o Method of constant stimuli used to determine a person’s absolute threshold for seeing a brief flash of light o He found a person could detect a flash of light that contained 100 photons  50 of these bounce off cornea or are absorbed by vitreous humour (jelly like substance that fills eye) and 50 reach retina  7 of these are absorbed by retinal part of visual pigment while the rest hit the larger opsin (not sensitive to light) or slip between visual receptors  This means that a person sees light when only 7 visual pigment molecules are isomerized, these 7 photons hit 500 receptors thus making it highly unlikely that any 2 photons would hit the same receptor o Hecht’s conclusions:  A person can see a light if 7 rod receptors are activated simultaneously  A rod receptor can be activated by the isomerization of just 1 visual pigment molecule o Enzyme cascade- An enzyme is a biological chemical that facilitates chemical reactions. The sequence of reactions triggered by the activated visual pigment molecule is called the enzyme cascade Pigments and Perception - Rod and cone visual pigments also shape aspects of our perception - Distribution of rods and cones in the retina: o Fovea- Small area of the retina that contains ONLY cones, contains only about 1% of the retina’s cones  When we look directly at an object it falls on the fovea o Peripheral Retina- The rest of the retina contains BOTH rods and cones  Many more rods than cones in peripheral retina o Macular Degeneration- Condition, most common in older people, that destroys the cone-rich fovea and a small area surrounding it creating a blind-spot in central vision o Retinitis Pigmentosa- Condition that degenerates the retina by attacking the peripheral rod receptors resulting in poor peripheral vision, eventually sometimes the foveal receptors are attacked resulting in pure blindness— Passed along generations o Blind Spot- Area in the retina with no rod or cone receptors, located where the optic nerve leaves the eye  Not aware of blind spot because it’s off to the side of visual field, because a mechanism in the brain fills in the place where the image disappears (creates a perception that matches surrounding pattern), and each eye covers the blind spot of the other - Dark adaptation- Process where eye increases its sensitivity in the dark and occurs by keeping eye in darkness o Dark Adaptation Curve- A plot of how visual sensitivity changes in the dark (occurs in two stages—first rapid stage is due to the adaptation of cones and lasts for the first 3-4 minutes and a later slower one occurs with the adaptation of rods and starts at 7-10 minutes and lasts until 20-30 minutes) o Measured by having participant look at a point so the point falls on fovea, then a light off to the side will fall onto the rest of the retina (so it can test rods and cones), then participant turns light down until they can just barely see it (called light-adapted sensitivity)  After this, the same thing is done but in the dark (finds dark- adapted sensitivity); Since eyes are becoming more sensitive to light, the light is continually decreased until just barely seen o Light-Adapted Sensitivity- When participant can just barely see test light when eyes are adapted to light o Dark-Adapted Sensitivity- The sensitivity at the end of dark adaptation that is about 100 000 times greater than before adaptation o Rod-Cone Break- At 7-10 minutes of dark adaptation, the rods have caught up in sensitivity with the cones but then continue to adapt further. At this point, the rods control the person’s vision which is the rod-cone break o To measure only cone adaption, participant looks directly at light so it falls on the cone-rich fovea o To measure only rod adaption we need to measure a person with no cones and only rods o Rod Monochromats- People who have no cones due to a rare genetic defect o Visual Pigment Bleaching- When light hits the retinal part of the visual pigment molecule, it is isomerized triggering transduction and separating the retinal from the opsin; The process of seperation causes the retina to become lighter in colour o Visual Pigment Regeneration-. Slowly, the molecules begin to regenerate while some are still being bleached in the light (unless in the dark when no light hits the retina); The process in which the retinal and opsin become rejoined  As they rejoin in dark, the pigment regains its darker red colour  Visual pigment regeneration for cones takes 6 minutes and 30 minutes for rods, corresponding to their subsequent dark adaptation times  Our sensitivity to light depends on the concentration of the visual pigment  Detached Retina- A condition that occurs when part of the retina becomes separated from the layer it rests on called the pigment epithelium which contains enzymes necessary for regeneration  Visual pigment can’t regenerate and person is blind in area of visual field served by this area of retina  Usually caused by eye or head injuries - Spectral Sensitivity- Person’s sensitivity to light at each wavelength across the visible spectrum o Monochromatic Light- Light with only a single wavelength, used to test a person’s spectral sensitivity— Measure the threshold for seeing light at different parts on the spectrum  Threshold for seeing light is lowest at middle of spectrum  Spectral Sensitivity Curve- Converting the threshold into sensitivity results in this curve— Use the equation “sensitivity=1/threshold”  We measure cones sensitivity by having people look directly at test light (so it falls on fovea) and rods by waiting till eye is dark adapted (b/c rods are most sensitive in dark) and presenting test light to side of fixation point  Rods are more sensitive to short wavelength light than the cones (rods most sensitive at 500nm and cones at 560nm)— Therefore as we go through dark adaptation we become more sensitive to short wavelength light (light nears to blue and green end of the spectrum)  Purkinje Shift- The shift from cone vision to rod vision that causes enhanced perception of short wavelengths during dark adaptation o Absorption Spectrum- Plot of the amount of light absorbed by a substance versus the wavelength of the light  Differences in spectral sensitivity are due to the absoption spectra of visual pigments  3 absorption spectra for the cones because there are 3 different cone pigments (each i
More Less

Related notes for Psychology 2015A/B

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.