2. Perception Flashcards
What is perception? How does it differ from sensation?
acquisition and processing of sensory information in order to interact with the world
guides an organism’s actions
Sensation: passive process of bringing information
from the outside world into the body and brain
Perception: active organization and interpretation
of sensory information into something meaningful
What are the 2 key types of perception?
Visual perception
Auditory perception
What is perceptual segregation and perceptual organisation?
distinguishing boundaries of overlapping objects in our environment
What is the Law of Prägnanz in perceptual organisation?
we typically perceive the simplest possible organisation
What are the 4 Gestaltist laws of perceptual segregation?
1) Law of proximity
2) Law of similarity
3) Law of good continuation
4) Law of closure
What is the law of proximity in perceptual organisation?
visual elements that are physically closer together tend to be grouped together
What is the law of similarity in perceptual organisation?
perceptually similar elements will be grouped together,
What is the law of good continuation in perceptual organisation?
Group together elements that require the fewest interruptions to form a line
What is the law of closure in perceptual organisation?
Missing parts of the figure are filled in to complete the figure.
What is figure-ground segregation?
Refers to the division of the visual environment into figure (have distinct form) and ground (no distinct form). The contour between figure and ground appears to belong to the figure.
Which do we pay more attention to and process more? Figure or ground?
Figure.
Evidence - Faces goblet illusion
Performance was better when the vertical or slightly tilted line was presented to the figure (as perceived by the participant) than the ground.
Which two gestaltist laws are most applicable to real life in perceptual organisation?
law of proximity (distance)
law of good continuity
Is figure-ground segregation more dependent on innate capacities or experience?
Innate capacity. When shown atypical and ambiguous shape contours, observers showed rapid and flexible learning.
What did gestaltists argue about the sequence of figure-ground segregation and object recognition?
Assume that figure-ground segregation always precedes object recognition. But this assumption is not entirely supported.
What did gestaltists conclude about the processes of figure-ground segregation and object recognition?
Processes involved in figure-ground segregation resemble the processes involved in object recognition, but is not always the case. They involve slightly different processes.
What is pattern recognition?
Identification or categorization of two-dimensional patterns. Generally involves matching information from visual stimulus with information stored in memory.
What is one intriguing feature about pattern recognition?
Flexibility. How we can recognise the letter ‘A’ across large variations?
What are the 2 theories in explaining pattern recognition?
Template theory
Feature theory
Describe template theory in explaining pattern recognition.
Argues that we have fixed templates stored in LTM corresponding to each visual pattern we know.
The template that provides the closest match to the stimulus input helps us recognise a pattern. Assume that there is more than one template for each letter and digit
Describe the normalisation process of the template theory?
To recognise the letter ‘A’, rotate and scale the stimulus to a standard position, and then map it onto the underlying representation/template in your mind.
What is a limitation of template theory in explaining pattern recognition?
Cannot account for the flexibility exhibited by humans in pattern recognition. Once u deviate from the template a bit you cannot recognise the pattern anymore. When stimulus belongs to ill-defined category (eg. buildings), no single template could possibly suffice.
Describe feature theory in explaining pattern recognition.
Argues that a pattern consists of a set of specific features. Helps us infer patterns based on characteristics rather than superimposing stimulus onto template.
What is an advantage of feature theory over template theory.
Can account for variation. Can identify visual stimuli that vary in size, orientation, and minor details as instances of the same pattern.
Describe the study in support of feature theory. (Neisser)
participants task was to identify target letter (eg. ‘Z’) as fast as possible.
Condition 1: distractor letters share same features as target letter (eg. straight lines) XTYZL
Condtion 2: distractor letters don’t share features as target letter (eg. rounded) ODZBS
performances was faster in condition 2
What is one key assumption of feature theory that may not hold true?
Assume that pattern recognition involves specific processing followed by more general/global processing to integrate information from the features. In reality, global processing can precede specific processing.
Describe the study by Navon which highlights that global processing can precede specific processing.
Forest before trees. (H & S)
Performance speed with the small letters was greatly slowed when the large letter differed from the small letters. In contrast, decision speed with the large letter was NOT influenced by the nature of the small letters.
Findings support the view that we often see the global structure before the features.
Name 3 types of cells involved in feature detection. What are these cells known as?
1) simple cells (orientation selective)
2) complex cells (moving contours; direction selective)
3) end-stopped cells (stimulus length & orientation)
Feature detectors. (Hubel & Wiesel)
What is a limitation of feature theory?
Overemphasis on bottom-up processes. Does not account for context and expectations. (top-down)
“object superiority effect” - Context provides useful information and makes the target stimulus more perceptible. Even if its using the same feature detectors to detect the same line, it matters if the line was part of a coherent form or not.
How does the “word-superiority effect” explain the importance of top-down processes?
A letter string is presented briefly followed by a pattern mask that inhibits further processing. Participants will be asked , “which of these 2 letters was in the 3rd position?”. (eg. A vs T)
Performance is better when the letter string forms a word than when it does not.
What is the “pseudoword superiority effect”?
Letters are easier to identify when presented in pseudowords (ie. pronounced nonwords such as “MAVE”) There is some overlap between spelling patterns in the pseudowords and genuine words (eg. “SAVE”, “GAVE”). This overlap benefits identification of the letters in the pseudoword in a top-down fashion.
Why is visual object recognition so complex?
objects vary enormously in their visual properties (eg. colour, shape, size)
wide range of viewing distances.
Which theory is used to explain object recognition?
Recognition-by-components theory (Irving Biederman)
What does the Recognition-By-Components Theory argue about object recognition?
Argued that objects consist of geons/geometric ions (basic 3D shapes) About 36 different geons that can be arranged in limitless combinations due to the different spatial relationships between them. Information about geons is stored in LTM.
The recognition-by-components theory proposes that geons are viewpoint-_____?
viewpoint-invariant
An object’s geons can be identified from many viewpoints
The recognition-by-components theory emphasises what process?
Emphasis on bottom-up processes. BUT Top-down processes (dependent on expectations and knowledge) more important when object recognition is difficult.
Describe an evidence to show the importance of concavities in an object’s contour in recognition.
Object recognition was much harder when parts of the contour providing information about concavities were omitted, as opposed to when other parts of the contour were omitted.
What are the limitations of the Recognition-By-Components Theory (geons)? (4)
1) Theory only accounts for unsubtle perceptual discriminations.
2) Doesn’t account for flexibility of geons (eg. clouds)
3) Based on assumption that processes in object-recognition are viewpoint-invariant. Not always the case
4) Neglects role of top-down processes
Define viewpoint-invariant and viewpoint-dependent.
Viewpoint-invariant: object recognition is equally rapid and easy regardless of the angle from which the object is viewed.
Viewpoint-dependent: object recognition is generally faster and easier when objects are seen from certain angles.
Object recognition is sometimes viewpoint dependent and sometimes viewpoint-invariant. In which context is each mechanism used?
Viewpoint-invariant mechanisms – more important when making easy discriminations. Easy task.
Viewpoint-dependent mechanisms – more important during more difficult within-category discrimination. Difficult task.
Visual processing involves which pathways in the brain?
occipital lobe –> inferotemporal cortex
Visual processing involves which pathways in the brain?
occipital lobe –> inferotemporal cortex
How do neurons respond for objects with high invariance?
Neurons responding almost equally strongly to a given object regardless of its orientation, size etc.
Neuronal selectivity supports which notion of object recognition?
Cognitive neuroscience supports the notion that object recognition can be either viewpoint-invariant or viewpoint-dependent. Viewpoint-dependent and viewpoint-invariant information can also be combined cooperatively to produce object recognition. We typically make use of all available information in object recognition.
Neuronal selectivity supports which notion of object recognition?
Cognitive neuroscience supports the notion that object recognition can be either viewpoint-invariant or viewpoint-dependent.
What are the 2 disorders of object recognition?
1) apperceptive agnosia - deficits in perceptual processing
2) associative agnosia - Perceptual processes are intact, but have difficulties accessing relevant knowledge about objects from long-term memory.
How to distinguish apperceptive agnosia from associative agnosia?
Assess patients’ ability to copy objects they can recognise.
Apperceptive agnosia - cannot copy
Associative agnosia - can copy
What is another issue associated with visual agnosia?
Problems with top-down processes.
Cannot use top-down knowledge of structure of visual scenes to guide her eye movements. Inspection of her eye movements revealed that she failed to focus on the areas most likely to contain the object.
Does face recognition involve different processes from object recognition?
Most evidence suggest that faces are processed differently from other objects.
Face recognition involves more holistic processing (integrating information across the whole object). Information about specific features can be unreliable because different individuals share similar facial features (eg. eye colour) or individuals’ faces can change (eg. skin shape, mouth shape).
Does face recognition involve different processes from object recognition?
Most evidence suggest that faces are processed differently from other objects
What is the part-whole effect? (context of face recognition)
Memory for a face part is more accurate when presented within the whole face rather than on its own. In contrast, recognition performance for house features was very similar in whole- and single- feature conditions.
What is the composite face illusion and what does it show?
The top halves look slightly different (even though they are identical) because it is natural to integrate information from both half faces in a holistic way. Applies more for misaligned horizontal faces than misaligned vertical faces. Occurs because vertically misaligned faces are more biologically plausible than horizontally misaligned faces.
What is prosopagnosia?
A condition mostly caused by brain damage in which there is a severe impairment in face recognition in with little or no impairment of object recognition.
What is a possible reason for prosopagnosia?
Person may have suffered damage to a part of the brain specialized for processing faces (FFA). Suggest that different processes and brain areas underlie face and object recognition
What are the 2 theories of face recognition? Briefly describe each theory.
1) Bruce & Young’s Model of face recognition
- when we look at a familiar face …
familiarity information –> personal information –> name
2) Modified/Simplified Model (Duchaine & Nakayama)
- face detection –> structural encoding (process face features) –> face memory (match to memory representation) OR emotion/gender etc.
- facial identity first before facial expression
What are the 2 theories of face recognition? Briefly describe each theory.
1) Bruce & Young’s Model of face recognition
- when we look at a familiar face …
familiarity information –> personal information –> name
2) Modified/Simplified Model (Duchaine & Nakayama)
- face detection –> structural encoding (process face features) –> face memory (match to memory representation) OR emotion/gender etc.
What is a key factor in determining super-recognisers of faces?
Genetic influence (twin studies)
What is the difference between visual imagery and visual perception?
Visual imagery - Involves forming mental representations of an object in the absence of the relevant stimulus in the environment. - Relies on top-down processes Visual perception - Relies on bottom-up processes
What is the Charles Bonnet Syndrome?
A condition in which patient experiences detailed visual hallucinations not under their control. They believe that visual perception has occurred even in the absence of an external stimuli. Associated with increased activity in brain areas specialized for visual processing (eg. FFA). suggests that hallucinating may involve similar processes to visual processing.
Why don’t most people confuse images (imagery) with perceptions? (2)
1) We deliberately construct images (active process), which is not the case with perception. (passive)
2) Images typically contain much less detail than perception
Why is visual imagery useful to us?
Allows us to answer ‘what if’ questions by making explicit and accessible the likely consequences of being in a specific situation or performing a specific action
What are the 2 theories used to explain visual imagery and visual perception?
1) Perceptual anticipation theory (Stephen Kosslyn)
2) Propositional Theory (Zenon Pylyshyn)
What does perceptual anticipation theory propose/assume?
- Assume that visual imagery resembles visual perception. (emphasize similarities) Mechanisms used to generate images involve processes used to anticipate perceiving stimuli
- Depictive representations: Information within an image is a depictive representation that is organized spatially in the same way as information perceived physically in real life.
According to perceptual anticipation theory, where in the brain area depictive representations found?
“visual buffer” - early visual cortex in the occipital area where spatial organization of brain activity resembles that of the imagined object. (V1, V2)
What is the difference between visual representations in the “visual buffer” for images and perceptions?
perceptions - depends on external stimulation
images - depends on non pictorial, propositional information stored in LTM.
According to Pylyshyn, what did propositional theory argue about performance on mental imagery tasks?
Argues that performance on mental imagery tasks involves tacit knowledge (ie. knowledge not generally accessible to conscious awareness), rather than depictive representations. Tacit knowledge is “knowledge of what things would look like to subjects in situations they imagine themselves in”. in form of propositions, which represent meaning in an abstract form. But this view is not well supported.
If visual perception and visual imagery involve similar processes, they should influence each other. What are the two types of effects possibly involved?
Facilitative effects - Content of perception and image is the same
Interference effects - Content of perception and image is different
What is binocular rivalry?
When two different stimuli are presented one to each eye, only one is consciously perceived at any given moment.
If one stimuli is presented shortly beforehand, that ________ the chances it will be perceived in the binocular rivalry situation.
increases
Describe an evidence for facilitation effects in binocular rivalry (ie. content perception and image is the same)
Presented observers with either a green vertical grating or a red horizontal grating. They were then later subject to the binocular rivalry condition. The facilitation effect was obtained and was greatest when the orientation of the grating in both conditions were the same. Even when first grating was imagined rather than perceived, a similar facilitation pattern was observed. Suggests that visual imagery involves similar processes to visual perception.
Visual perception and visual imagery generally involves which brain area?
Early visual cortex. Possibly involve similar processes.
processes.
What are the factors influencing whether early visual cortex is activated during visual imagery? (3)
1) nature of task
2) sensitivity of brain-imaging technique
3) shape-based vs scanning tasks
How does nature of task influence whether early visual cortex is activated during visual imagery?
Tasks requiring participants to inspect fine details of visual images were much more likely to be associated with activity in early visual cortex
How does sensitivity of brain-imaging technique influence whether early visual cortex is activated during visual imagery?
More sensitive brain-imaging techniques (eg. fMRI) –> can better detect brain activation than less sensitive ones (eg. PET)
In shape-based vs scanning tasks, in which tasks is the early visual cortex more likely to be activated during visual imagery?
shape-based
scanning tasks that imagine object in motion involve more spatial processing which is associated with different brain areas.
Which area in early visual cortex is specifically causally involved in visual imagery?
BA17 (V1)
Brain areas activated during _____ is a subset of those activated during _____. What does this suggest?
Imagery; perception
Suggests that visual imagery involves only some of the processes involved in visual perception.
What is the key difference between imagery and perception?
Information contained in images can’t be used as flexibly as perceptual information. (tutorial activity - wine glass, clock) Suggests that images often consisted of simplified structural descriptions omitting important aspects of the object being imagined. Information available in visual perception is more detailed and can be used more flexibly.
Some patients have intact visual perception, but impaired visual imagery. Which part of the brain is damaged?
Damage to to left temporal lobe because much of our knowledge of concepts is stored there
Likely that visual images are generated from information stored in temporal lobes.This generation process is not needed for visual perception.
What is Anton’s syndrome (“blindness denial”)?
Intact visual imagery; impaired visual perception
Blind people are unaware they are blind and may confuse imagery with actual perception. Primary visual cortex destroyed, but patient generated visual images so vivid they were mistaken for real visual perception.
What is mental rotation?
Imagining what would happen if an object was rotated from one orientation to another. If we use mental rotation, the time taken to decide whether two objects are identical will be longer the more rotation is required. Involves spatial and motor processing.
What are possible reasons why males often outperform females on mental rotation tasks?
1) practice effects from video games
2) hunter-gatherer theory
3) social factors (education, encouraging boys to play with certain toys)
Which brain areas are involved in visual imagery?
Primary visual cortex in occipital lobe & temporal lobe which stores object and concept information
Which brain areas are activated during mental rotation?
Posterior parietal lobe - Parietal areas contain spatial maps; associated with spatial processing
Motor areas in the posterior frontal cortex - Mental simulation of physical actions involved in object rotation
What are the 2 visual systems/pathways we possess?
Ventral pathway ('what') - identification of objects
(goes to IT)
Dorsal pathway ('where') - movement and visually guided action. (goes to MT)Using the Müller-Lyer illusion (2 lines), explain how using each visual pathway will affect the mean illusion effect?
Ventral pathway ('what') - illusion will be present if they just look at which line is longer.
Dorsal pathway ('where') - illusion effect will be reduced when people are allowed to physically point and touch the two figures.
Mean illusion effect was 4 times greater with vision-for-perception system than vision-for-action system.What is inattentional blindness?
Failure to notice an unexpected object appearing in a visual display. (eg. the gorilla in the midst of students)
What is change blindness?
Failure to detect that an object has moved, changed, or disappeared
What is change blindness blindness?
Describes our wildly optimistic beliefs about our ability to detect visual changes. We greatly overestimate our ability to detect visual changes in our environment.
When is change blindness most likely to occur? (central vs marginal interest)
Change blindness more likely to occur when object is of marginal interest
Comparing intentional approach (people expect a change) vs incidental approach (people don’t expect a change), when are observers more likely to expect a change?
intentional approach
BUT even with intentional approach, a substantial proportion of people still fail to detect changes. Indicates that our long-term memory for complex scenes can be much less accurate than we believe.
In terms of similarity to relevant stimuli, when is change blindness most likely to occur?
Findings suggest that an unexpected object (ie. gorilla) attracts more attention when it is similar to task-relevant stimuli, so it is more likely to be detected.
Type change – object is replaced by another object from a different category
Token change – object is replaced by another object from the same category
In which situation is change detection better?
Type change.
What causes change blindness? (2 reasons)
1) attentional processes - We show change blindness when we do not pay attention to the changed object.
2) Inability to retain detailed information for long periods of time - visual representations decay rapidly over time
Does perception necessarily require conscious awareness?
NOPE.
Unconscious/subliminal perception - perception occurring even though the stimulus is below the threshold of conscious awareness
How to decide whether observer is consciously aware of the stimulus? (subjective vs objective threshold)
Subjective threshold – individual’s failure to report conscious awareness of a stimulus. Most obvious measure to use
Objective threshold – individual’s inability to make an accurate forced-choice decision about a stimulus (eg. guess above chance level whether it is a word)
Observers often show “awareness” when assessed via objective threshold, even when it does not exceed subjective threshold.
Which is more valid to use? Subjective or objective threshold?
Objective threshold - less subjective and biased. Evidence for subliminal perception based on objective threshold is more convincing
Participants were shown either letter ‘b’ or ‘h’ in 2 conditions. Comparing long (15ms) vs short (10ms) interval conditions under threshold (no conscious awareness), which produced more accuracy?
long. Suggests that there was some conscious awareness and processing of the stimulus in long interval condition, just that participants lacked awareness of that processing.
How much visual processing occurs below the level of conscious awareness?
participants were presented with pictures of invisible faces or houses (not consciously perceived). Patterns of brain activation indicate that participants could predict the identity of the picture (face vs house) with almost 90% accuracy. Suggests that even stimuli that cannot be perceived consciously can be processed by the visual system.
What is blindsight?
A condition produced by brain damage to early visual cortex (V1) in which there is behavioural evidence of visual perception in the absence of conscious awareness. Can perceive motion, and location of objects!
What is affective blindslight?
The ability to discriminate between emotional stimuli presented below the level of conscious awareness. Opens up the possibility that blindsight patients have some conscious vision but simply set a high threshold for reporting awareness.
4-point scale of conscious awareness: “Clear image” -- 100% correct “Almost clear image” -- 72% correct “Weak glimpse” -- 25% correct “Not seen” -- 0% correct What do the findings suggest about the reason for blindsight?
Degraded conscious vision could account for blindsighted patients’ ability to perform at above-chance levels on visual tasks.
What is categorical perception? (hint: ‘ba’ and ‘da’)
The tendency for speech sounds intermediate between two phonemes to be perceived as one phoneme or the other. (Present listeners with sounds /ba/ and GRADUALLY moving towards /da/. We expect listeners to report a gradual change from perceiving one phoneme to the other. But they tend to report an abrupt shift in perception.) Also present in non-speech sounds.
What is a possible mechanism for the categorical perception effect?
Amplification effect - When two auditory stimuli of opposite sides of the boundary (eg. /ba/ vs /da/) were presented at the same time, differences in brain activation of the 2 stimuli were strongly amplified.
Musicians have stronger categorical perception for chords, it shows the role of exposure and practice. How does this explain categorical perception for phonemes?
Categorical perception phonemes is so strong possibly because we are all expert listeners to phonemes.
How does categorical perception create a context effect in real life?
eg. ‘dash’ vs ‘tash’
An ambiguous phoneme was more likely to be assigned to a phoneme category when it produced a word, than when it did not.
What is the difference in brain activation when processing speech and non-speech sounds?
Speech perception depends partially on motor processes, which differs from the processing of nonspeech sounds. Involve lips in articulation.
What evidence supports the fact that both speech and non speech sounds generally involve similar mechanisms?
1) Both influenced by top-down processes
2) Similar patterns of brain activity when both speech and nonspeech are processed
What are 2 key differences between speech vs non-speech perception?
1) Processes involved in speech perception tend to be more complex, hence more brain areas are activated during speech perception
2) Motor processes are more important during speech perception
Segmentation problem - how do listeners manage to work out where one word ends and another begins? (4)
1) Certain sequences of speech sounds are never found together within english words (eg. never found tgt) Suggest a likely boundary between words
2) ‘Possible-word’ constraints in English (eg. consecutive consonants NOGO)
3) Stress - In English, the initial syllable of most nouns and verbs is stressed
4) Word context - Lexical cues (ie. information about syntax) were more useful in quiet conditions
What is the McGurk effect?
The combining/blending of visual and auditory information when the two sources of information are in conflict.
speech + mouth = ‘ba’
speech ‘ga’ + mouth ‘ba’ = ‘da’
The McGurk effect is influenced by what process?
Mcgurk effect is influenced by top-down processes based on listeners’ expectations.
What is the phonemic restoration effect?
A type of context effect where listeners use contextual information to identify sounds/words. They tend to replace and interpret a meaningless sound with a phoneme that fits into the context of the sentence.
It was found that the *eel was on the shoe. (heel)
It was found that the *eel was on the table. (peel)
What does a large N400 in sentence processing indicate?
Mismatch between meaning of processed word and context of sentence.
What does motor theory predict about speech perception?
Listeners effectively mimic the articulatory movements of the speaker. This helps to assist speech perception by reducing variable information (eg. tone of voice)
Provide an evidence for motor theory.
- Greater activation of listeners’ tongue muscles when presented with words that require strong tongue movements when pronounced.
- harder to perceive speech if parts of the motor system were disrupted by rTMS. (left premotor cortex)
What findings can motor theory NOT account for?
- Some brain-damaged patients whose motor speech system has been almost destroyed nevertheless have an essentially intact ability to perceive spoken words
- 6-8 month infants perform reasonably well on syllable detection tasks even though they have extremely limited expertise in producing speech
(Suggests that mimicking speakers’ articulatory movements when trying to understand speech is merely one strategy among many)
