Lecture 4: Sensing and Perceiving Flashcards
What is transduction?
1) Outside world sends us signals
2) Sensory transducers (eyes, ears, nose, tongue, skin) encode and convert into bodily sensations (proximal stimuli).
3) Process may take place over vast distances (far senses).
4) Process may take place at the point of contact (near senses).
What is symbolism?
1) Transduction recodes outside world into sensation.
2) We recode environment.
3) In case of human perception, we assume specific brain states give rise to specific perceptual experiences.
What is organisation?
1) Neurones at each stage of processing arranged in highly organised way according to nature of sense.
What is selectivity?
1) Both at sensory and neural level.
2) Sensory: in terms of transduction.
3) Neural: where individual cells prefer certain types of stimulation above others.
What are hierarchies?
1) Perceptual processing involves series of stages.
2) One representation is transformed into another.
3) Each sense contains multiple, hierarchically organised processing stages/
4) basic - medial - complex.
What is tailoring?
1) Our sensory transducers are specifically tailored for its environment and for carrying out survival behaviour.
2) Allow us to view the world in a different way.
3) We have two eyes, nose near mouth, etc.
What is an absolute threshold?
minimum amount of stimulation required to evoke perceptual sensation.
What is a ‘just noticeable difference’ (JND)?
minimum amount of differential stimulation required to note change between sensations.
What is sensory adaptation?
same level of intensity does not generate the same continuous level of response.
-constraint of perception.
What are decision rules?
1) frequently perceptual information is incomplete or ambiguous.
2) therefore, stimulus processing from the bottom-up cannot account fully for perception.
3) top-down decisions also need to be made.
4) receiving information from environment requires decision making.
How much of the electromagnetic spectrum can we experience?
- We are only privy to an incredibly small portion.
- Despite limited access, we are able to perceive in environments which differ 100 million times in terms of light availability.
Can we see radio waves or x-rays?
No, but they are all present as light visible to humans.
What is wavelength?
Distance travelled after one complete oscillation of a certain wave.
How do we ‘see’?
1) Light reflected from objects travelling in straight line ast 30,000 km per second.
2) enter through the pupil.
3) bend via lens.
4) reaches convergence on retina.
What is the sclera?
- tough white bit
- protection
What is the cornea?
- transparent area
- allows light in
What is the iris?
- controls pupil size
- gives eye colour
What is the pupil?
-opening at centre of iris.
What is the lens?
- transparent structure
- focuses light
What is the retina?
- light sensitive cells
- back of the eye
What are the properties of the centre of the eye?
Photoreceptor: Mainly cones Receptive field size: Small Resolution: Good Sensitivity: Poor Optimal condition: Photopic (light).
What are the properties of the periphery of the eye?
Photoreceptor: Mainly rods Receptive field size: Large Resolution: Poor Sensitivity: Good Optimal condition: Scotopic (dim).
How many cones per eye?
6 million.
How many rods per eye?
120 million.
What are most people in terms of viewing colour?
Trichromatic: red, green and blue.
-relative activity of three pigments explain secondary colours.
What are dichromates?
Only have two of three cones (G vs R).
Do we have the same amount of all the colour cones?
- We have fewer B cones than G or R cones.
- Cone pigments become less the further we move from the fovea.
What are tetrachromatics?
- some species have four cone pigments.
e. g. sensitive to UV light
Which colours oppose each other?
R vs G
Y vs B
What is trichromacy theory?
Establishes the different cones available to us.
What is opponency theory?
Establishes how B, G and R cones (and other colour sensations) interact.
What is a colour deficiency test?
- equates lightness and colour
- attempts to assess difficulties in cone or opponent processing.
- Short-wavelength deficiencies are less common than middle- and long-wavelength deficiencies.
- Both can be acquired or genetic.
What can Glaucoma and diabetes affect?
S cones.
What can alcoholism affect?
Reduce long-wave sensitivity due to lack of vitamin B12.
What factor can lead to blue-green confusion?
Age.
What are Gestalt principals?
- Bottom-up processes can supply us with ‘untainted’ information about our sensory world.
- Top-down processes can help or hinder the interpretation of our sensory world via expectations and heuristics.
What is similarity?
Similar things appear to be grouped together.
What is good continuation?
Points that, when connected, result in straight or smoothly curving lines seen as belonging together.
-the lines tend to be seen as following the smoothest path.
What is common fate?
Things that are moving the same direction appear to be grouped together.
What is familiarity?
Grouping is more likely when we recognise what we see
How do Gestalt Principles operate?
- as heuristics rather than algorithms.
- Heuristics: tend to be fast and produce the correct result most of the time.
- Algorithms: tend to be slow and produce the correct result all the time.
- Humans=busy so prefer heuristics.
What is top-down information?
historical context
immediate context
conceptual knowledge
language
What is bottom-up information?
proximal stimulation of sense organs and neural coding.
What are the two types of depth cues?
Monocular and Binocular.
What are the features of a monocular depth cue?
Occlusion
Size: Objects that cover a smaller retinal size tend to be further away than objects that cover a larger retinal size.
Linear perspective: There appears to be an overestimation of the extent to which size interacts with receding distance.
Higher up further away
Texture gradients: Textures tend to become more dense the further away they are in space.
What are the features of a binocular depth cue?
Oculomotor
-Convergence accommodation.
Retinal disparity.
What does audition function as?
An early warning system in the service of vision.
Auditory stimulation:
-Perceived from locations not currently within focus of attention.
-In contrast, only visual stimulation within our current field can be perceived.
How large is the range of frequencies we can experience?
Only a small selection.
What properties of waveform should relate to perceptual experience?
Height of waveform: refers to intensity,
Length of waveform: refers to frequency.
What does density of waves mean?
More dense= higher
Less dense= lower
What does the size of waves mean?
Small waveform= quieter
Large waveform= louder
How do air molecule pressure and sound intensity rekate to each other?
Direct relationship.
Large pressure waves relate to loud sounds.
Small pressure waves relate to softer sounds.
What is a decibel?
- dB
- Measurement of sound amplitude (not loudness).
- The scale is weighted such that the range of human auditory experience can be represented meaningfully on the same scale.
What are the features of the OUTER EAR?
DIRECTIONAL MICROPHONE
Pinna: Numerous flaps on each side of your head. These folds are useful for vertical localisation.
Auditory canal
Ear drum: The first in a long series of transduction.
Cerumen: Ear wax. Predominately found in the outer ear and moves slowly outwards, helping to clean the ear.
What are the features of the MIDDLE EAR?
IMPEDANCE MATCHING AND OVERLOAD PROTECTION
Hammer (malleus)
Anvil (incus)
Stirrup (stapes)
-Ossicles bones transmit vibration from large to small areas.
-Fluid inside oval window reduces amplitude by about 30dB.
-Ossicles transmit recouping about 23dB.
-In about 1/120th of a second, the eardrum can stiffen, leading to a 30dB reduction.
-This helps when exposed to very loud sounds.
What are the features of the INNER EAR?
FREQUENCY ANALYSIS
Cochlea
Organ of Corti
Basilar Membrane
-Behind stapes, the oval window provides entry to cochlea.
-The base has high frequency, the apex low frequency, sensitivity.
-It comprises of three separate chambers all filled with fluid, with the round window providing some pressure release.
-The basilar membrane lies on the bottom of the organ of Corti, which separates the bottom and middle chambers of the cochlea.
What are the two methods of sound localisation?
1) Inter-aural intensity differences
2) Inter-aural time differences
What are inter-aural intensity differences?
Sounds from the left will be louder at the left ear than the right ear.
-The head attenuates high frequencies (low frequencies move round the head).
What are inter-aural time differences?
Sounds from the left will arrive earlier at the left ear than the right ear.
-We are sensitive to about 10 millionths of a second.
What is the thalamus?
Relays sensory signals to cortex (not smell).
What is the hypothalamus?
Controls endocrine (hormone) system.
What is the hippocampus?
Hub relating to learning, memory and space.
What is the cerebellum?
Regulates balance and body control.
What is the brain stem?
Regulates breathing and heart rate.
What are A-delta fibers?
Carry sharp or pricking pain.
What are C fibers?
Carry dull or burning pains.
How do many pain receptor neurones transmit pain?
Via the neurotransmitter substance P.
What is the (spinal) gate control theory of pain?
- Substance P pumped out due to banging your elbow.
- Non-painful cutaneous stimulation such as rubbing the elbow stimulates endorphins (natural opiates).
- The gate closes, reducing the message of pain.
What can the gate theory also account for?
The control of pain on the basis of emotional or cognitive factors.
-A central mechanism can control the interpretation of sensation, again closing the gate.
What is perception?
An active process involving competition between external physical information, expectations and belief.
