What have psychologists learned about perception from optical illusions

Psych 105: ZAPS Labs

Lab 1- Split Brain

Introduction

· Common misconception by media: that people are right or left-brain dominant.

· Misconception started with concept of lateralization (diff parts of brain have different functions; L & R hemispheres have own specializations)

· Lateralization dates back to roman empire where greek physician/surgeon Galen of Pergamon noticed gladiators suffered language impairments when injured on left side of skill.

· Left hemisphere = dominant for language; Right Hemisphere = global spatial information

· 2 hemispheres connected by corpus callosum (large fiber of axons)

· nerve impulses travel from left brain to right brain through corpus callosum

· “Split-brain” operation patients= doctors sever corpus callosum to prevent severe epileptic attacks from spreading to both sides of brain.

Discussion:

· 2 important brain facts:

· The right hemisphere of the brain interprets information presented in the left visual field, and vice versa.

· The right hemisphere of the brain controls the left hand, and vice versa.

· Split brain patients:

· have difficulty recognizing/naming objects when info is presented in left visual field (which is processed by right hemisphere)

· RH has enough language capability to comprehend simple words, doesn’t have “phonological” (speech) capabilities to allow work of object to be spoken.

· So while RH can read the word and direct left hand to pick up correct object, the patient can’t state the name of object.

· When word presented in right visual field, patient’s LH can easily process word (since language abilities reside in LH), direct patient say word out loud, and cause right hand to find object.

· BUT when there is mismatch between visual field that the word is presented to and hand the patient is asked to use, the patient is unable to grasp the hidden object behind the screens, even if word was processed in the LH, and easily recognized.

· Gazzinga (first discovered in 1960’s)

Learning Check:

1. The word banana appears on the left screen, and the split-brain patient is told to use her left hand to select the object named on the screen. Will she be able to fetch the banana? (Answer = Yes)

2. The word banana appears on the left screen, and the split-brain patient is told to use her right hand to select the object named on the screen. Will she be able to fetch the banana? (Answer: No)

3. The word banana appears on the right screen, and the split-brain patient is told to use her left hand to select the object named on the screen. Will she be able to fetch the banana? (Answer: No)

4. The word banana appears on the right screen, and the split-brain patient is told to use her right hand to select the object named on the screen. Will she be able to fetch the banana? (Answer: Yes)

Lab 2: Ponzo Illusion

Introduction:

· Our brains perceive depth in 2D images through depth cues .

· Our brains automatically & instantly apply these 2D patterns to same mechanisms it uses to figure out spatial relationships btwn objects in real 3D world.

· Retina : all direct info you visually see

· When image of something reaches retina, size is dependent on distance of object from observer.

· Retinal image will appear smaller the farter the observer is from object.

· Once brain receives the sensory info from retina and interprets it, you perceive that the objects would be same size in 3D. (even though yellow car seems further than red car)

Data:

· Goal- to adjust length of bottom line to match perceived length of top line in context of the ponzo illusion and then examine numerical error percentage to see how “off” people are.

Discussion:

· Ponzo illusion (optical illusion)

· Demonstrates how brain relies on “depth perception” to guess properties of object it cannot directly sense.

· When asked to adjust bottom to match top, most people overadjust (making bottom longer than top.

· This is bc in ponzo illusion, the oblique (slanted) vertical lines provide brain with distance cues by making image appear 3D.

· we perceive 2 oblique lines (parallel, converging into distance - like railroad tracks) thus making top appear further than bottom.

· This means: when given 2 horizontal lines of same length, brain will perceive top line as longer.

· Explanation: even though 2 equally long horizontal lines take up same space on retina, our visual system perceives the top line to be longer – bc if top line was actually further away, it really would be longer than a closer line that took up same space on retina.

· Size constancy – brain’s use of contextual info

· Objects closer take up more retina than objects further away. BUT we know that nearby cars and far cars = same size.

· Why? Brain uses other distance cues to override fact that closer cars take up more visual space.

· “Judgement error” in ponzo occurs bc you’re exposed to artificial situation that tricks brain into improperly applying a visual heuristic (a rule of thumb/ size constancy) that is usually reliable so brain automatically trusts it.

· Muller-Lyer Illusion :

· the vertical lines don’t appear to be of equal length. The v shaped lines at ends of vertical lines provide contextual depth info for visual system.

Learning Check

1. A psychological scientist asks study participants to indicate whether the green line at the front corner of the wall pictured here is longer than, shorter than, or equal in length to the green line at the back corner of the wall. Participants regularly say that the front line is shorter than the back line (even though the two are perfectly equal in length). The participants’ brains are using ___________ to guide perception.

a. (answer choices: rulers, context cues about depth, previous experience, geometric insights; answer = context cues about depth)

2. The process we call perception involves our eyes sensing objects in our world and our brain interpreting the information that our eyes sense. Keeping this definition in mind, which of the following is a true statement about the Ponzo illusion?

a. Answer choices: our eyes lead us to perceive something that is not actually true, our eyes mistakenly sense information about line length, the ponzo illusion is due to errors in both sensation and perception, the brain leads us to perceive something that is not actually true; answer = brain leads us to perceive…)

3. A real-life visual illusion is the “moon illusion.” When the moon is close to the horizon, the full moon seems larger than it does when high up in the sky. Rationally we know that the moon does not change size according to its position in the sky. Based on what you have learned about optical illusions, why do you think the moon illusion occurs?

a. Answer choices: repeated exposure to movies that show large moons as backdrops in romantic scenes train the brain to misperceive the size of the moon in real life, only children who havnt had a lot of opportunity to observe and perceive the moon are likely susceptible to the moon illusion, when the moon is near the horizon, objects on Earth, which are near the moon on your retina, lead to a misperception of depth and size – the brain discerns the low moon as closer and thus bigger than the moon high in the sky; answer: last one)

Lab 3- Attentional Blink

Introduction:

· Every day we continuously process info from surroundings. We take in more info than we can process because our attentional capacities at given moment are limited.

· We ignore certain stimuli and attend to others.

Data:

· In the alphanumeric sequences, each stimulus shown for 90 ms before next one replaced it. There were 4 different types based on distance between letters.

· Observations: 1. Able to recognize first target letter. 2. Recognition of target letter was affected by how many numbers appear between the two target letters.

· Reeves & Sperling – we process info episodically.

· Process 1st target letter as part of an attentional “episode” followed by suppression of attention (attentional blink) for about 180-450ms.

· If % of correct id’s for 2nd letter was significantly less than for 1st letter, you experienced attentional blink

· Your attention was occupied in processing the 1st letter so anything appearing after that suffered in comparison.

· Summary: when you perceived and attended to the first letter, your brain took time to fully process it. If the second letter followed the first one immediately or soon after, the time it took to process the first letter likely spilled over into the second letter’s critical period of processing. The overlap in processing between the two letters caused a “perceptual blind spot”, and prevented you from attending to the second letter.

Discussion:

· Our attentional system = selective attention .

· Ability to focus our attention on one event/piece of info/ while blocking out background noise/irrelevant stimuli.

· Aka “cocktail party phenomenon”

· Suggests that we can ignore irrelevant stimuli but important stimuli like our name being called is likely to stand out amongst background noise.

· Attentional blink = manifestation of selective attention.

· When we focus on one event, it takes few moments to fully recover our info and shift to a novel stimulus.

· Ability to process any info (especially sequences where occurrence of AB is inconsistent) is affected by factors: alertness and motivation to complete task.

· Reason for AB not understood but tendency to engage in selective attention allows us to maximize processing info we deem most relevant.

· Divided attention = when our attentional resources are allocated to at least 2 pieces of info at once.

· Ulric Neisser & Robert Becklen had subjects watch a double-exposure movie – 2 movies overlapped on same screen- to evaluate attentional capacities.

· 1 group (selective attention group) – tasks with detecting important events in only one of the videos;

· 2nd group (divided attention group) told to detect events in both.

· Results: divided attention missed a lot more info and made 8x number of detection errors than selective attention group.

· Selective attention followed by attentional blink can cause even more errors in processing.

· Optimum strategy for allocating attention = flexibility (which permease selective or divided attention depending on what task demands)

Learning Check:

1. Studying for an important exam while watching tv is not very efficient bc it is an example of: (selective attention, divided attention, attentional blink, cocktail party phenomenon)

a. Answer: divided attention)

2. Our attentional systems cope with the overwhelming amount of info that we encounter on a daily basis by engaging in selective attention, and by extension, attentional blink. (True)

3. Being able to drive a car while you carry on a convo with a friend in passenger seat is explained by: (answer: ability to automatize driving and dedicate the majority of your attention to the conversation)

4. Which of the following scenarios is an example of attentional blink?

a. Answer: a waiter is telling 2 friends about the daily specials when a neighboring table erupts in laughter. The friends ask the waiter to repeat the last few items because their attention was diverted by the sudden loud laughs.

Lab 4 – Serial Position Effect

Introduction:

· working memory—the processing system that keeps information available for current use

· can only maintain 5-9 pieces of information for 20-30 seconds

· serial position effect - form of memory bias in which our ability to recall a given item from a series depends on its relative position within that series.

Discussion:

· graph = serial position curve

· demonstrates how people tend to recall items from beginning and end of a list.

· Serial position effect involves 2 diff. relative positons within a list

· Primacy effect- better recall of items at beginning of list

· Recency effect: better recall at the end.

· Why are our recall for middle of list items lower?

· Rundus and Atkinson (1970) = found our ability to mentally rehearse items from beginning of a list explains our enhanced recollection of them.

· We cannot rehearse items from middle of list as frequently as those at the beginning (hence our decreased recollection of items in middle)

· Rehearsing items over and over again leads to the storage of these items in long-term memory.

· Rundus and Atkinson concluded that the recency effect must take place by means of a different cognitive mechanism than that of the primacy effect.

· While the primacy effect takes place when items enter long-term memory through frequent rehearsal, the recency effect occurs because the items near the end of a list are still present in working memory at the time of recall.

· In this way, we can easily retrieve the last few items presented in a series.

· If there is a delay in time between the presentation of a list and the participants’ recall of that list, the recency effect disappears, and only the primacy effect remains (Bjork et al., 1974).

· This occurs because the items from the beginning of the list remain in long-term memory, whereas the items at the end of the list have since disappeared from working memory at the time of recall.

· People who can no longer form new long-term memories—a condition called anterograde amnesia—observe the recency effect when there is no delay, but not the primacy effect. (Carlesimo et al., 1996).

Learning Check:

1. True or False: When you remember the first few items from a list better than items in the middle of the list, this effect takes place because the first items were still present in your working memory upon recall.

a. False - Better memory for the first few items in a list, or the primacy effect, takes place because you can rehearse these items and transfer them to your long-term memory.

2. Which of the following best describes the serial position curve for an experiment conducted with a delay between the presentation of a list and participants’ recall of that list?

a. High percentages of recall for the first few positions in the list and low recollection for all other items in the list.

b. High percentages of recall for the first few positions in the list, low recollection of the middle items of the list, and high recollection of items at the end of the list.

c. High percentages of recall in the middle of the list and low recollection of items at the beginning and end of the list.

i. Answer: a. When there is a delay between the presentation of a list and recollection of that list, we still observe the primacy effect, but we no longer observe the recency effect because items at the end of a list are no longer in working memory at the time of recall.

3. A friend tells you the seven-digit passcode to enter her home. How long will this information remain in your working memory if you do not rehearse it?

a. Answer: 20-30 seconds.

Lab 5 – False Memory

Introduction:

· Memory distortion: a collection of phenomena that demonstrate how our long-term memories are not always permanent

Data:

· Critical lure: a centrally related word was absent from the initial list. For example, the word sleep did not actually appear in the initial list of sleep-related words. However, that centrally related word, called the critical lure, was present in the list of words to choose from.

· False memories: memories are imperfect; can be forgotten or distorted.

Discussion:

· Researchers find that participants generally recall seeing the critical lure with just as high a frequency as words that actually appear on the original list.

· People report feeling very confident that they indeed saw the critical lure in the original list (Weber & Brewer, 2004).

· This is an important finding because it reminds us that the certainty with which someone states a claim cannot be used as a gauge for how truthful that claim is.

· Because our memory is limited, we have to store the things we want to remember in an efficient way.

· One way to do this is to use a schema—a cognitive structure that helps us perceive, organize, process, and use information.

· You may also have event schemas (also known as scripts), such as for a birthday party: This might consist of the guests entering, unwrapping gifts, singing a birthday song, and eating cake.

· Our schemas help us navigate the world efficiently; without schemas, our world would be a very overwhelming place.

· The words in this experiment were all meaningfully related to a relevant schema. The schema activation you experienced enabled you to create false memories by giving you enough information to make you believe that the lure word was also present.

· 1. This type of memory distortion = suggestibility, which is defined as the development of false memories from misleading information.

· 2. Memory bias -the changing of memories to fit current beliefs or attitudes.

· 3. Source misattribution can happen with the time, place, people, or circumstances involved with a memory.

Learning Check:

1. Which of the following is a key finding from research using memory tests like the one in this ZAPS lab?

a. People rarely feel confident in their assessments of whether lure words appeared on the original lists

b. Memory although not perfect is generally highly reliable

c. People believe that the lure word was present in the list just as frequently as other words that actually did appear in the list.

d. People very accurately remember the content of word lists.

i. Answer: c

2. A cross-country driver decides to eat at a local restaurant she has never heard of. She walks in and sees a counter that contains cash register machines; a menu hangs above the counter. Behind the counter, employees wearing headsets and paper hats hustle to and fro, pulling food from a service window and placing it onto trays. These images will most likely trigger a ________ that will lead the traveler to believe she should ________ .

a. Schema; wait by the door until a host shows her to her seat where a waiter will take her order

b. Schema; order at the counter and then seat herself

c. Semantic association; wait by the door until a host shows her to her seat where a waiter will take her order

d. Semantic association; order at the counter and then seat herself.

i. Answer: b

Lab 6 – Sentence Verification

Introduction:

· semantic category knowledge—general knowledge of facts, ideas, meanings and concepts.

Data:

· Based on reaction times in sentence verification tasks, Collins and Quillian hypothesized that our knowledge network for animals looks like this:

· The semantic distance between two words is determined by the connections in the network and is defined as the shortest interval between these two words

· For instance, the semantic distance between “canary” and “bird” is 1, while between “canary” and “animal” it is 2. Thus, the semantic distance in the sentence “A canary has skin” is 2.

· Research indicates that people take longer to make a decision about a correct sentence as the semantic distance increases.

· The semantic distance between two words is determined by the connections in the network and is defined as the shortest interval between these two words

· For instance, the semantic distance between “canary” and “bird” is 1, while between “canary” and “animal” it is 2. Thus, the semantic distance in the sentence “A canary has skin” is 2.

· Research indicates that people take longer to make a decision about a correct sentence as the semantic distance increases.

Discussion:

1. network has a hierarchical structure.

a. If an item is found under one concept, which is itself nested within another higher concept, the original item belongs to both higher-level concepts.

i. because the concept “canary” belongs to the class of “bird”, then “canary” also belongs to the higher class of “animal” because “bird” belongs to “animal”.

2. principle of inheritance applies in it.

a. This means that features are only stored once and as high as possible in the hierarchy.

i. In the figure above, for instance, “lay eggs” is not stored at “canary” but at “bird”, since all birds lay eggs. Likewise, "breathes" is stored at the level of “animal”, since all animals breathe (whether with lungs or through gills).

3. typicality effect - Researchers routinely find that people react more quickly to sentences like “A robin is a bird” than to sentences like “A chicken is a bird”. This is because a robin is a “better” example, or a more typical exemplar for the category “bird”, than a chicken.

a. The typicality effect points out the limitations of Collin and Quillian’s model, which does not effectively account for the strength of category membership.

b. Strength of category membership is not simply a function of the distance from concept to concept within the hierarchy.

4. spreading activation model—(Collins & Loftus, 1975), is that it explains not only the typicality effect, but also many other effects that have been revealed through sentence verification tasks.

a. features need not be duplicated in multiple hierarchies; “red” is associated with “apple” and “fire engines”, as well as “roses” and “sunsets”.

Learning Check:

1. According to the network proposed by Collins and Quillian, common characteristics that different breeds of dogs share (e.g.: fur, tail, sharp hearing) will appear once and as high up as possible in the network. What is this concept called?

a. Similarity

b. The principle of inheritance

c. Typicality effect

d. Spreading activation

i. Answer: b

2. True or False: During flu season, people are more likely to ask, “Do you have any Kleenex?” than “Do you have tissues?” This is best explained by the typicality effect.

a. True

3. The Collins and Quillian model proposes that categorical information is organized hierarchically. What is one important difference between this model and a spreading activation model?

a. The relationship between concepts in a spreading activation model can strengthen or weaken depending on typicality and frequency of occurrence.

b. The relationships between concepts in a spreading activation model are determined by the principle of inheritance

c. There are no differences between the Collins and Quillian model and a spreading activation model.

d. The relationship between concepts in the Collins and Quillian model can strengthen or weaken depending on typicality and frequency of occurrence.

i. Answer: a

Lab 7 – Lexical Decision

Introduction:

· All the words you know are stored in your mental lexicon

· Mental lexicons organize words by meaning.

· Morpheme- smallest unit of language that carries a meaning (i.e.: suburb, subconscious)

Data:

· David Meyer and Roger Schvaneveldt (1971) proposed a serial-decision model which suggests that the physical layout of the letter strings on the screen makes you decide on them sequentially.

· You first decide whether the top letter string is a word, and then you move onto the bottom letter string.

Discussion

· In order to judge whether a string of letters is a real word, you have to search your mental lexicon to see if stored somewhere

· Each word in your lexicon has a threshold that much be satisfied for the word to be recognized.

· Common words (high frequency words) = low thresholds and low response times

· Infrequent words = require more activation, have higher thresholds, and higher response times.

· Repetition priming

· Semantically related words also get partial activation. = semantic priming

· Explained by theory of spreading activation (when a concept is activated, activation spreads from that concept to nearby concepts)

Learning Check

1. Research conducted on homographs (ie: bat or minute) in lexical decision tasks predicts that you are likely to ________.

a. Activate multiple meanings of the words, and partially activate closely related words

b. Take longer to understand the word because it has an ambiguous meaning

c. Activate one meaning of the word, which is not necessarily decided by the context.

d. Access only the meaning of the word that is appropriate in the given context

i. Answer: a

2. Words are most likely stored in the mental lexicon by semantics, so that table would be closer to chair than it would be to tape.

a. Answer: true

3. Hearing or reading a word frequently increases the ease and speed of its recognition because of this phenomenon in lexical decision.

a. Frequency priming

b. Repetition priming

c. Semantic priming

d. Serial priming

i. Answer: b

Lab 8 – Analogical Representation

Introduction:

· Mental representation: a mental “copy” of some phenomenon present in the world

· Key components that form the basis of human thought

· Analogical representation: mental image of the object possesses certain physical attributes that match the actual physical attributes of the real-life object.

· Cooper (1975) asked participants to determine whether two nonsensical, figures were the same or mirror images of each other.

· They showed participants both simple and complex nonsensical figures, and compared the reaction times of both types of trials.

· Found that there was no significant difference in their responses to simple versus complex nonsensical figures.

· Findings suggest that reaction time depends upon the relative angle of rotation between the two figures and not their complexity.

· Finke (1989) discovered that when we rotate an object mentally, it occurs much in the same way as when we rotate an object in real, physical space. He stated that visual imagery has transformational equivalence with rotating items in real space.

· This means that if it takes us longer to rotate an object 200 degrees than it does to rotate it 100 degrees in real space, it will also take us longer to rotate a mental representation of the same object 200 degrees versus 100 degrees.

· Symbolic representation: does not share physical qualities with the concept it represents because it is abstract in nature.

Learning Check

1. Picture your childhood bedroom. The mental image you just created is an example of what type of mental representation?

a. Pictorial representation

b. Symbolic representation

c. Analogical representation

i. Answer: c

2. When rotating a glass pyramid 240 degrees with our hands, it takes a longer amount of time than it does to rotate it 40 degrees. According to Finke’s concept of transformational equivalence, it will take us _____________ amount of time to rotate a mental representation of a pyramid 240 degrees than it would to mentally rotate it 40 degrees.

a. A longer

b. A shorter

c. The same

i. Answer: a

3. It takes people longer to mentally rotate complex nonsensical figures than it does for them to rotate simple nonsensical figures.

a. True or false

i. Answer: false - As Cooper (1975) found, the relative difference in the angle between two figures determined the amount of time it took for participants to mentally rotate them. The complexity of the figures did not affect mental rotation time.

Lab 9 -Decision Making

Introduction:

· Decision making: the selecting of the best alternative from among several options

· Expected utility theory: dominant theory of decision making held that people simply calculate the “expected utility” or value, of the possible choices for any decision they need to make and choose the option that maximizes the desired outcome

· Predicts what individuals would do if they were entirely rational vs. prospect- what they actually do

Experience

· Prospect theory: people evaluate psychological prospects of the choices, rather than the objective expected values.

· Weigh the fear of losing $100 against the hope of gaining $125

· Loss aversion: people are generally eager to avoid costs than potentially gain benefits

· Framing: the way a choice is worded (framed) changes the psychology of how people perceive the choice, and prospect theory says it is the value of the choices’ prospects that determine what people do, as opposed to the objective expected values.

· Framing effect ex: whether a choice is framed in terms of gains or losses. People prefer lotteries, which frame the prospect in terms of potential gains, to straight-up bets which frame the prospect in terms of how much one might lose

· Anchoring: when making their estimates, people start from the “anchor”

· Causes ones judgment to be affected by the results of a previous estimate, even though both judgments were intended to have been made independently.

· When making decisions under conditions of uncertainty, we automatically apply heuristics (rules of thumb) to try to reduce the uncertainty.

· Representativeness heuristic: the description of someone is representative of a stereotype/category so our intuitive heuristic tells us it seems plausible.

· Directs us to choose the most plausible conclusion when we are unsure of which conclusion is most probable.

· Availability: go with what comes to mind more readily. Works sometimes but not all the time

· Tells us to replace a question we cannot realistically answer with a similar question whose answer is more readily available.

Learning Check:

1. Consider the following gamble. A standard pack of playing cards, including 26 red cards (diamonds and hearts) and 26 black cards (spades and clubs), is shuffled, and the card on top of the deck is turned face up.

· If the face up card is red, the gambler wins $11

· If the face up card is black the gambler loses $9

Expected value theory predicts which:

a) Most people will accept the gamble

b) Most people will reject the gamble

c) People will be equally likely to accept or reject the gamble

I. Answer: a.

2. Consider the same gamble. Prospect theory predicts which?

a. Most people will accept the gamble

b. Most people will reject the gamble

c. People will be equally likely to accept or reject the gamble

I. Answer: b

3. In a 1997 experiment, participants were first asked whether the Indian leader Mahatma Gandhi died before or after a certain age, then were asked to guess the precise age at which Gandhi died. People who were first asked whether or not Gandhi died at age 9 gave an estimate (50 years) much lower on average than those who were first asked whether or not he died at age 140 (67 years). This experiment is a perfect example of which of the following?

a. The anchoring effect

b. Availability heuristic

c. Loss aversion

d. Representativeness heuristic

I. Answer: a

Lab 10 Sudden Insight

Introduction

· Problem solving: using info available to achieve a goal

· Insight: sudden realization of a solution to a problem

Discussion:

· Gestalt psychology = major focus was problem solving with insight

· Particularly interested in how cognitively restructuring a problem (seeing it in a new way) often leads to its solution

· Another way to successfully problem solve is by dividing task into subgoals.

· Mental set: most common tendency to persist with a tried and true strategy

· Can be useful but sometimes hinter us from finding a solution

Learning Check:

1. Which of these would a follower of Gestalt psychology be concerned about the least?

a. Seeing problems in a new way

b. Whether a problem is trivial or non-trivial

c. Insight problems

d. The cognitively restructuring of problems