Perception Flashcards
What is Fourier Analysis for Vision?
Fourier analysis is a technique that can be used to break down any image into simpler sinusoidal gratings of various spatial frequencies.
Who said that the CSF reflected the combined activity of many independent mechanisms called filters?
Campbell and Robson 1968
What is Campbell and Robson’s interpretation of the CSF?
The came up with the multiple filter’s model.
What is the difference between low spatial frequency and high spatial frequency filters?
Low- encode coarse outline/overall shape
High- fine spatial structure/ detail
What did Campbell and Robson (1968) do in their study?
Evidence from psychophysical experiments.
Measured contrast detection thresholds for simple sinusoidal gratings of a given frequency. compared to detection for square-wave gratings(image).
What is special about square wave gratings?
The are images and so can be fourier analysed int a set of sinusoidal gratings of increasing frequency and decreasing contrast.
What does the Multiple Filters Model of the CSF predict?
Patterns are detected on the basis of the outputs of various spatial frequency filters.
How was Campbell and Robson’s 1968 study evidence for the multiple filter’s model?
Detection thresholds for square-wave gratings weren’t the same as sinusoidal gratings.
What is adaptation?
Prolonged viewing of a high contrast patter that makes subsequently viewed patterns hard to see.
Blakemore & Campbell 1969 found that adaptation is spatial frequency selective. How does this support the multiple filter’s model?
By the CSF curve only dropping in contrast sensitivity at the adapted frequencies; this shows that multiple systems must be involved.
The human retina contains 5 major types of neurons, what are they?
Photoreceptors (rods and cones)
Bipolar cells-transfer information from photoreceptors onto ganglion cells
Horizontal cells-collects signals from photoreceptors
Amacrine cells-transmit signals from one ganglion cell to another
retinal ganglion cells(RGC)
How does the Duplex theory of retinal processing say that the visual system adjusts to different environments?
Pupils constrict
Cone driven phototopic( light) system-high acuity and low sensitivity
Rod driven scotopic (dark) system- low acuity, high sensitivity
How can we investigate what type of stimulus ganglion cells respond best to?
single cell recording. Allow us to measure the firing rate of a ganglion cell.
How are the ON(excitatory) and OFF(inhibitory) regions arranged in a ganglion cell?
Centre- Surround Antagonism
OFF responses form a ring surrounding the ON response region.
What purpose does the Centre-Surround system serve?
It helps the retina distinguish edges.
How is the LGN associated with ganglion cells?
Layers 1 & 2 of the LGN are called the magnocellular layers and receive input from M cells.
Layers 3-6 are called the parvocellular and receive input form P cells.
K cells are sandwiched in between.
What is a retinotopic map?
An orderly map of the retina that preserves the topography of the retina. Each of the 6 layers of the LGN.
In colour perception what is a metamer?
A metamer is used to describe sensory stimuli which are physically different but perceptually equivalent.
Humans have 3 types of cone types. This is called Trichromacy. What are they?
Blue/short wavelength(S)
Green/medium(M)
Red/long(L)
Parvocellular retinal ganglion cells have chromatically opponent receptive fields. What does this mean?
The centre of their receptive field may be stimulated by red light whilst the inhibitory surround is excited by green light.
What is the principle of univariance regarding photoreceptors?
Any single photopigment is colour blind since an appropriate combination of wavelength and intensity can result in an identical neural response.
Who proposed the trichromatic theory of vision?
Young-Helmholtz
What is the topography of the three cones like on the retina?
On the retina there are much fewer S(blue) cones than L(red) or M(green).
Individuals with congenital colour defects have a normal number of cones but perform like Dichromats instead of…
Trichromats
The LGN relays information between the retina and the visual cortex. It is sensitive to spatial frequency but not…
orientation
Name some differences in marvocellular and parvocellular cells?
Marvocellular- larger, largest receptive fields, sensitive to motion not colour
Parvocellular-smallest receptive fields, colour sensitive not motion sensitive & best spatial resolution.
What is the difference between simple, complex and hyper complex cells?
Simple cells- certain orientation within the receptive field.
Complex cells-any orientation within the receptive field.
Hypercomplex cells- specific to orientation and contour length.
Which part of the visual cortex contains ocular dominance and orientation?
V1- which contains simple, complex and hypercomplex cells.
What is Pareidolia? Paras & Webster(2013)
False alarms often for faces causing us to see faces everywhere.
What is the Domain specificity hypothesis in face recognition?
nature debate- we are born with dedicated mechanisms for face recognition.
Schmalzl et al, 2008- prosopagnosia shows that face perception can be distinguished from object recognition. What is prosopagnosia?
Inability to distinguish faces acquired through damage to the occipito-temporal regions.
Yin et al found that faces are much harder to recognise upside down than other objects. What is this effect called?
The Inversion effect
Tanaka & Farah (1993) evidence for configural/holistic encoding showed that…
When ppts were trained on intact faces they were more likely to recognise the correct part when presented in the whole face. Holistic processing of faces.
The composite effect demonstrates…
compulsory holistic perception but only in upright faces
What is the opposite of the Domain specificity hypothesis?
The expertise hypothesis-.
Michel et al, 2006 Other-race effect shows that..
asian and caucasian ppts show a greater composite effect for faces of their own race than the other. This implies that extensive experience is necessary.
Which part of the brain in involved in object recognition?
Ventral stream in the inferior temporal cortex.
What is the simplest model of object recognition?
Template-matching model
How is the feature-detector model different from the template-matching model?
Feature-detector model is states that we recognise objects by assembling their features rather than the whole object.
Marr and Nishara’s structural detection model proposed stages of image processing. What are these?
- Viewer centred and object centred processing
- primal sketch which detects edges
- A 2 1/2D sketch
- 3D model
Terms used are primitives
Bierderman proposed a theory to what these primitive cones are composed of. He called them…
Geons.
What are the sensory receptors in Mammalian skin?
Epidermis, Dermis, pascinian corpuscle, meissner corpuscles etc
What are the cutaneous touch receptors?
Mechanoreceptors ( meissner corpuscle, pascinian corpuscle, merkel discs & ruffini endings) are touch receptors that respond to pressure or indentation of the skin.
What are the temporal properties of mechanoreceptors?
Slowly adapting fibres respond to a persistent stimulus whereas rapid adapting fibres respond only to the onset and termination of a stimulus.
What are the spatial properties of mechanoreceptors?
Receptive fields in the skin have concentric organisation (excitatory centre and inhibitory surround). Some large some small.
What pathway carries somatosensory information?
The lemniscal pathway- axons enter the dorsal side of the spinal cord then the thalamus on the contralateral side then to the somatosensory cortex in the parietal lobe.
What information is gained through active touch?
Tactile and proprioceptive information(Haptics)
Are there specific receptors and pathways for pain?
Pain results from the stimulation of a receptor called a nociceptor. The spinothalamic pathway is the pain pathway.
Can we explain the variable nature of painful experience?
Melzack and Wall’s gate-control theory attempts to explain this.
Describe Melzack and Wall’s Gate theory .
We have fast touch and slow pain fibres that connect with the SG and T cells in the spinal cord.
T cells send pain information to the brain.
SG acts as a gate to allow or inhibit T cells.
Activity in fast fibres close the SG gate(touch but no pain) and the slow fibres open the gate(pain).
What are the characteristics of taste and smell?
taste(gustation) and smell(olfaction).
Chemoreceptors are involved.
What are Henning’s 4 basic taste qualities?
salty, sour, sweet and bitter.
What are the receptors that mediate taste perception?
microvilli
What are the neural pathways for taste pathways?
3 sets of afferent nerve fibres carry taste information from taste buds:
chorda tympani, glossopharyngeal and the vagus.
How does the brain differentiate between different substances?
One solution is the Cross-fiber theory by Pfaffman & Erikson.
It states that most neurones in the taste system respond to several stimuli but each one is tuned best to a particular substance. The pattern of firing is different thus this can be coded by the brain.
What are Henning’s proposed 6 primary odours?
- fragrant
- putrid
- ethereal
- burned
- resinous
- spicy
What are the receptors that mediate smell perception?
Olfactory receptors located on the olfactory epithelium. Evidence supports the ;lock and key hypothesis.
Does smell interact with taste?
Yes. Flavour is a combination of taste and smell. Mozel & Murphy & Cain investigated this and found that without smell the ability to identify foods by taste alone is poor.
