Perception Flashcards
What was the assumption about mind and body until the mid 1800’s?
an assumption that the mind and the body are separate from each other
What did Gustav Fechner reveal about the mind and body in the 1850’s?
the mind and body are not independent and so the mind can be studies by measuring the relationship between changes in physical stimulation and a person’s experience
What was proposed in ‘elements of psychophysics’, published in 1860 by Fechner?
proposed a number of methods to study the relationship between mental and physical. this included the proposal of three techniques to measure thresholds
Define Psychophysics:
the scientific study of relationship between physical stimulus and perceptions evoked by it
Define Absolute Thresholds:
measures the minimum of a stimulus that can be perceived by one of our senses
Define Difference Thresholds:
measures the smallest difference between two stimuli a person can detect
What is the steps of psychophysics deconstructed?
-physical stimulus (how do we select and present the stimulus)
-task (what does the participant have to do)
-measure (how do we categorise behaviour)
What are the three methods to measure thresholds?
method of limits, method of adjustment, method of constant stimuli
How is the threshold determined in the Method of Limits?
experimenter presents stimuli in ascending or descending order and determines the cross over point where perception changes. the threshold is the average of the cross over points
How is the method of adjustment carried out and how effective is the method?
the participant adjusts the stimulus intensity. It is a relatively fast method but it is frowned upon for it’s accuracy
What is the most accurate method of measuring threshold and why?
Method of constant stimuli because it involves more observations and the stimulus is presented in a random order to reduce order and expectation effects.
Describe the method of constant stimuli and how the threshold is reached:
the experimenter is presented stimuli of different intensities in a random order. participants indicate their perception, the stimulus is chosen so that the weakest is never detected and the strongest is always detected. The threshold is the intensity at which stimulus is detected 50% of times
How many intensities are typically involved in the method of constant stimuli?
5 to 9
What is a quick solution to the expectations of subjects and order effect?
Forced Choice Procedures (Fechner)
What do Forced Choice Procedures entail and how is the threshold determined?
stimulus is presented side by side and participants choose which side contains the stimulus (ie. grating) until it is too faint to see. Due to the guessing chance, if participants are unable to see the grating at all they should obtain 50% correctly. The Threshold is therefore determined at 75% correct
Explain the difference between 2AFC and 2IFC in the Forced Choice Procedure:
2AFC: the stimulus is presented at the same time
2IFC: the stimulus is presented one after another
What is the up-down method that measures perception?
Adaptive Staircase Procedure
How is the Adaptive Staircase Procedure carried out and how is the threshold reached?
intensities that are included in the threshold are presented. the procedure begins with perceivable stimulus and if correctly identified the intensity is decreased until an error occurs and the intensity is increased again. The threshold is determined by averaging over the transition and reversal points
What are three classical psychophysical tasks used to determine thresholds?
-detection: is the stimulus there?
-discrimination: which stimulus is stronger?
-matching: adjust the stimuli so they look/sound/feel the same
What is weber’s Law?
The ratio between the difference threshold and the intensity of the standard is constant
What does the difference threshold depend on?
the size of the standard stimulus
What is the accuracy of Weber’s Law determined by?
As long as the stimulus intensity is not too close to the absolute threshold
What does Weber’s Fraction depend on?
the sensory dimension measured as the value of standard stimulus is different between dimensions
How is perception measured above threshold?
Magnitude Estimation (Stevens, 1957)
What happens in Magnitude Estimation?
participants rate the size or intensity of a stimulus on a numerical scale in relation to a standard stimulus
True or False: Doubling Physical Intensity doubles the perceptual experience
False
Explain response compression:
the increase in perceived magnitude is smaller than increase in stimulus intensity
Explain response expansion:
the increase in perceived magnitude is larger than increase in stimulus intensity
What is Steven’s Power Law?
a power function used to describe the relationship between intensity of a stimulus and perception of its magnitude
What is the issue measuring perception when comparing two people?
The response of two different observer’s in constant stimulus where they have different thresholds. The response criteria between people may lead to erroneous conclusions about perceptual sensitivity
What are the four types of responses in the Signal Detection Experimenter?
hit or miss (when stimulus is actually present), false alarm or correct rejection (when the stimulus is absent)
Describe the perceptual approach:
perceptual representations of the world- measures detection and discrimination performance of visual stimulus
Describe the evolutionary/ecological perspective (active vision):
guidance of actions, primary role of the visual system is to guide our actions. vision is needed to explore and manipulate the world around us
What does the Perception-Action model refer to (AD Milner and MA Goodale, 1995)?
how perception and action relate in the human brain
What are the origins of the perception-action model?
origins in animal and neuropsychological research based on cortical processing mechanisms
what is the main idea of the perception-action model?
the idea that people’s perception of the world does not always follow the same rules as their behavioural interactions with this world
‘two visual stream model’ and ‘two visual systems hypothesis’ are other names for which model?
The Perception Action Model
What are the two streams involved in perception that are initiated after visual input?
the dorsal stream, and the ventral stream
what are the effects of lesion to the ventral stream?
lesion impairs recognition and identification of objects
what are the effects of lesions to the dorsal stream?
lesions impair perception of spatial relations between objects
Out of dorsal and ventral, which stream is conscious and which is unconscious?
Dorsal stream= unconscious
Ventral stream= conscious
What damage did Patient DF suffer, and how did this effect her? (agnosia)
Patient DF suffered bilateral lesions in area LOC of the Ventral stream. As a consequence she faced a visual form of agnosia where she struggled to recognise and identify objects
Despite visual agnosia, what abilities did Patient DF maintain in object perception?
she could still identify texture and colour of objects. her performance was normal in corresponding tasks for example when grasping to is able to adjust hand opening to object size
What region of the brain are the ventral and dorsal stream originated in?
the Primary Visual Cortex
What does the case of Patient DF provide evidence for?
suggests evidence that the ventral stream is important for perception such as recognizing size and shape of objects
True or False: dorsal stream damage is more common that ventral stream damage
true, ventral stream damage is very rare
What complications are associated with dorsal stream damage?
optic ataxia where patients struggle to perform visually guided actions but have no problem with perceptual tasks
What do studies of lesions to the dorsal stream provide evidence for?
evidence to suggest that the dorsal stream is important for visual guidance of actions
Describe double dissociation:
complementary effects of ventral and dorsal stream damages suggests the ventral stream mediates Vision for Perception, and the dorsal stream mediates ‘Vision for Action’
What are three limits of clinical case studies:
1) neuropsychological evidence on its own cannot prove the perceptual system is not involved in guidance of actions
2)patients may rely on different info or develop alternative strategies through brain plasticity
3)evidence is needed for the requirement of perception and vision for action in healthy brains
What do visual illusions initiate?
introduce a dissociation between conscious perception of size and real metrics of objects which are assumed to guide actions
Why are illusion studies not sufficient evidence of Perception-Action Systems?
results are controversial because distances between perception and action tasks can be explained without the assumption of distinct processing mechanisms
What part of the Perception-Action model is undisputable?
it is undisputed that ventral streams are relatively more important for perceptual processes and dorsal streams are more important for planning and guidance of actions. the degree of communications between the streams is controversial
What is the nature of modularity in the ventral stream?
neurons responding to similar stimuli are grouped together in brain areas
What is an example of the modularity in the ventral system in the brain?
Patient DF suffered deficits in perceiving form and shape however not all the ventral stream is damaged. Some patients with ventral stream damage that processes colour suffer from cerebral achromatopsia but have no problem processing shape
What is the difference in born or developed colour-blindness and colour blindness symptoms caused by cerebral achromatopsia?
colour blindness concerns actual colour receptors in the eyes whereas cerebral achromatopsia is caused by lesions to the ventral stream (brain damage)
What were the results of the study concerning response of neurons in a monkey’s inferotemporal cortex?
97% of the neurons in the face were face selective. cells responded to different views of monkey and human faces but had a much weaker response for other body parts
What is evidence for specialised face and object (double dissociation) in the ventral stream?
Prosopagnosia (unable to recognise faces but no agnosia for objects), and Object Agnosia (lose ability to recognise objects but no problem in recognising faces)
Describe the modularity in the dorsal stream:
based on nature of the actions that are guided by visual objects. most neurons in the dorsal stream do not fire unless some action is required towards a seen objects and there is modularity of certain movements
What was discovered regarding API neurons in the dorsal stream of monkeys (Murata et al., 2000)
the neurons are selective to shapes and specific grasp postures
What are the three main types of receptors in tactile perception and what do they respond to?
Mechanoreceptors: respond to mechanical stimuli i.e. pressure, stretching, vibration
Thermoreceptors: respond to temperature
Chemoreceptors: Respond to certain chemicals e.g. histamines
Why are Nociceptors undecidedly their own separate group of receptors?
they mediate perception of pain however they are potentially subtypes of chemoreceptors and mechanoreceptors
How are responses elicited from tactile receptors?
different types are distributed through the skin and respond to different touch stimuli and events
What type of receptor do the following subtypes belong to? : Merkel receptors, Meissner’s corpuscle, Pacinian corpuscle, Ruffini cylinder
Mechanoreceptors
For the following receptors; Merkel Receptor, Meissner’s Corpuscle, Pacinian Corpuscle, Ruffini Cylinder; describe the alternative labels (if any) size, borders, adaptation, stimulus, and distance to skin surface:
Merker Receptor: AKA Tactile disc. small receptors with sharp borders; slow adaptation; pressure, fine texture, and shape; close to skin surface
Meissner’s Corpuscle: AKA Tactile Corpuscle. small receptors with sharp borders; rapid adaptation; indentation, motion across skin; close to skin surface
Pacinian Corpuscle: AKA Lamellated Corpuscle. large receptors with diffuse borders; rapid adaptation; vibration and fine texture; deeper in skin
Ruffini Cylinder: AKA Ruffini Corpuscle. Large receptors with diffuse borders; slow adaptation; stretching; deeper in skin.
What are two ways to measure Tactile Acuity?
Two Point Threshold and Grating Acuity
Describe Two Point Threshold in Tactile Acuity:
classical measure in early touch research however vulnerable to confounds. The minimum separation between two points on the skin that are recognised as two point. This is the smallest discriminable difference between two points.
Describe Grating Acuity in Tactile Acuity:
Acuity for which orientation can still be accurately judged or at least 75% correct. Testing for horizontal vs vertical orientation. This is a more objective measure with no temporal effect.
What are the nature of the thresholds in Two-Point Threshold Method and Grating Acuity?
Grating Acuity Thresholds tend to be a bit lower in grating Acuity than the two-point method; 1mm vs 2-4mm
What do skin receptor properties determine?
Perceptual Experience when skin is stimulated
What is the Merkel receptor Mechanism?
respond to grooved stimulus patterns. the firing of the fibre reflects the pattern of grooved stimulus. this signals detail and texture
What is the nature of receptor density in sensitive body parts?
sensitive body parts have higher receptor density
What is better tactile acuity associated with?
higher density of Merkel receptors (most of the time)
What is an exception to ‘higher acuity for areas with higher density of receptors’, and what is this an example of?
The index finger pad has higher acuity than the pad of the little finger even though their receptor density is identical. These are cortical mechanisms
Aside from receptor density, what else contributes towards tactile acuity?
the size of the receptive fields of cortical neurons. Cortical neurons representing body parts with higher acuity have smaller receptive fields
What are the benefits of braille reading for tactile acuity?
intense braille reading can produce superior spatial acuity in both blind and sighted humans via changes in cortical representation
How does tactile acuity correlate with age?
Tactile acuity declines with age at a rate of about 1% a year
According to duplex theory of texture perception (David Katz), what cues does the perception of texture depend on?
Spatial cues: cues available to vision and touch. this is determined by size, shape, and distribution of surface elements (e.g. Braille letters)
Temporal cues: specific to touch. determined by the rate of vibration as skin moves across finely textured surfaces e.g. sandpaper.
What does perception of very fine textures require?
movements
Explain the study providing evidence for the duplex theory of texture perception:
Hollins and Risner (2000). Participants struggled to identify differences between two fine textures in static conditions but improved considerable when they were able to move their fingers over textures. Coarse surfaces were equally discriminable in moving and stationary conditions.
What is sensing fibre texture through temporal cues mediated by?
Perception of vibration
What did the adaptation paradigm involve?
temporarily inactivating different receptor types
Describe the procedure and the findings of the adaptation paradigm:
The Meissner Corpuscle, which responds to low frequencies, was adapted at 10 Hz for 6 minutes.
The Pacinian Corpuscle, which responds to high frequencies, was adapted at 250 Hz for 6 minutes.
The receptors were therefore deactivated.
After the adaption to 250Hz, vibration participants were unable to discriminate the two textures. This proves that fine texture discrimination depends on Pacinian Corpuscles
Why does touch provide a more reliable perception of surface texture than vision?
visually perceived surface texture is influenced by illumination. surfaces appear rougher with decreasing illumination angle. touch involves direct contact with a surface providing a more reliable assessment
How can touch become more accurate with very fine textures?
higher resolution and access to temporal cues
Describe the two afferent subsystems that mediate haptic perception:
Cutaneous/Tactile Input: Mechanoreceptors and thermoreceptors of the skin which mediate tactual experience
Kinaesthetic input: Mechanoreceptors embedded in the muscles, tendons, and joints which contribute to human perception of limb positions
What is usually involved in haptic perception?
active manual exploration
Why is haptic perception complex?
haptic perception requires close interplay between the sensory system (cutaneous sensations), the motor system (moving the fingers and hands), and the cognitive system (thinking about the information provided by sensory and motor systems)
Describe passive touch:
being touched. the ‘object’ is passively moved across the skin of the observer (no voluntary movement form the observer). this focuses perception on sensory/bodily responses such as skin sensation
Describe active touch:
touching objects. the observer moves actively with full control over their movements which engages haptic perception. Perception focuses on external object properties
In the somatosensory system theory, describe the ‘what’ and ‘where’ subsystem:
What= perception of material/surface properties. the systematic relationship between exploration actions and object properties. surface texture, compliance (deformability under force), thermal quality, weight, geometric properties (such as shape and size).
Where= where localisation can be referred to relative to
A) the sensory organ (where skin touch occurs depending on the spatial resolving capacity of the skin)
B) the environment (where space is a stimulus touched i.e. how do we localise points in space during haptic exploration when vision is unavailable)
Describe the ongoing debate regarding the somatosensory system:
there is a debate as to whether the somatosensory system can be divided into a what (perception of surface properties) and where (perceptual guidance of action, localisation of touch) subsystem
True of False: Haptic Space is anisotropic?
True, haptic space varies in magnitude depending on direction
What are the six most used exploration procedures assessing texxture, weight, hardness, volume, temperature, exact shape)? Lederman and Klatzky 1987
lateral motion (texture)
unsupported holding (weight)
pressure (hardness)
enclosure (global space and volume)
static contact (temperature)
contour following (global shape, exact shape)
How is the Pacinian corpuscles activated in manual exploration for Haptic Perception?
Optimal activation of neural responses enhance response of slow adapting Merkel receptors and create deep vibrations activating Pacinian Corpuscles
Describe the study that indicates use of two spatial reference frames:
Kappers and Koendering. task = adjust a test bar so it feels parallel to the standard bar.
Explain the two competing spatial reference frames?
Egocentric-when judging bar orientation this is related to the orientation of the hand touching the bar
Allocentric- orientation of the hand touching the bar differs depending on the location
Why is understanding affective responses to materials important?
understanding affective responses to materials can help to design human machine interfaces such as assistant robots or safe work tools
In Drewing and Colleagues (2017) study, what 6 perceptual dimensions and 3 affective dimensions were materials judged by?
6 Perceptual dimensions:
fluidity
roughness
deformability
fibrousness
heaviness
granularity
3 Affective Dimensions:
valence (pleasantness)
arousal (exciting/boring)
dominance
Why were fluid materials associated with higher arousal?
potentially due to less predictable skin stimulation
What materials were rated as least pleasant?
rougher materials
How does tactile acuity correlate with the density of Merkel receptors?
areas on the body with high acuity and high receptor density are also devoted a larger area of processing in the brain
why does the somatosensory homunculus have odd proportions?
areas on the body are represented disproportionally in the brain.
How is the S1 (Somatosensory cortex) organised? (Penfield and Rasmussen, 1950)
S1 is organised in maps corresponding to locations on the body
Describe the somatosensory homunculus:
Large areas for the hand and lips (which are most sensitive to touch). Small areas for legs and back (less sensitive). similar topographical representation in the motor cortex
What is meant by somatosensory cortex plasticity?
the map is not fixed. the homunculus varies based on individual experiences shaped by learning
What were the findings of classical experiments on owl monkeys regarding somatosensory plasticity? (Merzenich and colleagues 1987)
intensive stimulation of a skin area (3 months of training) causes an expansion of the cortical maps
What evidence from musicians supports neuroplasticity in humans? (Elbert et al. 1995)
violinists show enlarged somatosensory cortex of regions that receive touch from the tips of the left hand
Describe Focal Dystonia:
AKA Musician’s cramp. painless muscular incoordination. a neurological disorder characterised by loss of fine motor skilled movements during instrumental playing. the disorder is task specific to instrumental playing
What is a correlating factor with focal dystonia?
strong correlation between instrument group and localisation of the disorder. the hand with higher workload becomes affected and more often occurs in the dominant hand.
