Unit 6 - Visual Perception Flashcards
What is meant by a sensation?
The effects of a stimulus on the sensory organs.
What is meant by perception?
The elaboration and interpretation of a sensory stimulus based on, for example, knowledge of how objects are structured where:
Elaboration in this context refers to the process of adding detail or complexity to a sensory stimulus, e.g., by using stored knowledge
Interpretation is the process by which the brain interprets and makes sense of sensory information received from the environment
What is the retina?
The internal surface of the eyes that consists of multiple layers, with some layers containing photoreceptors that convert light to neural signals, and others consisting of neurons themselves
What is a rod cell?
A type of photoreceptor specialised for low levels of light intensity, such as those found at night.
What is a cone cell?
A type of photoreceptor specialised for high levels of light intensity, such as those found during the day, and specialised for the detection of different wavelengths.
Where is the highest concentration of cones? What is this, and what is it responsible for?
In the fovea
A small, central pit in the retina responsible for sharp, detailed vision
What is the blind spot? In what proportion are rods and cones present there?
The point in which the optic nerve leaves the eye
Neither of them is present at all
What are bipolar cells? What do they create through their connections?
Cells that behave in on of two ways: detecting light areas on dark backgrounds (ON) or detecting dark areas on light backgrounds (OFF)
A receptive field
What is the receptive field?
The region of space that elicits a response from a given neuron
What are centre-surround cells used for?
Advanced processes like detecting edges and orientations
What is the dominant route to V1 from the eyes called? What does it go through? What is the function of this organ?
The geniculostriate pathway
The lateral geniculate nucleus (LGN)
Processing station
What are the Konio (K) layers? What is their functional specialisation?
Lies between P and M layers
Unclear
What is the primary visual cortex (V1)? What is its function regarding the spatial relationships found on the retina? What is another important function of it?
The first stage in visual processing in the cortex
Retaining them
Combining simple visual features into more complex ones.
What are the 6 layers of the LGN?
Upper four layers are called the parvocellular (P) layers, responsible for processing fine details and colour
Lower two layers are the magnocellular (M) layers, responsible for processing movement and larger, less detailed aspects of the visual field.
Four main transformations done by the V1 on visual information:
Distinguishing between light and dark
Distinguishing colours
Distinguishing edges (abrupt changes in brightness and/or colour)
Distinguishing depth
What are simple cells?
Cells in vision that respond to light in a particular orientation or points of light along that line
What are complex cells? How do their receptive fields compare to those of simple cells? Is stimulation required across the entire length of the receptive field? How can they be acquired?
Cells in vision that respond to light in a particular orientation but do not respond to single points of light
Larger receptive fields
Yes, it is.
By combining many simple cells
What are hypercomplex cells? How are they built?
Cells in vision that respond to particular orientations and particular lengths
From the responses of several complex cells
What does the path from the retinal ganglion cells to the suprachiasmatic nucleus involve?
Info about night or day feeding the biological clock
What are two alternative pathways through which visual information travels from the eye to different parts of the brain?
The Retinal Ganglion Cells to the Suprachiasmatic Nucleus
The Retinal Ganglion cells to the Superior Colliculus and Inferior Pulvinar
What is hemianopia? What damage is associated with it?
Cortical blindness restricted to one half of the visual field
Damage to primary visual cortex in one hemisphere
What does the path from the retinal ganglion cells to the superior colliculus and inferior pulvinar do?
Provides orienting stimuli for automatic body and eye movements, working faster than V1
What is quadrantanopia?
Cortical blindness restricted to a quarter of the visual field
What is the ventral stream in vision? Where does it start and end? What are its three specialisations?
A pathway extending from the occipital lobes to the temporal lobes
Object recognition, memory, semantics
What is scotoma?
A small region of cortical blindness
What is retinotopic organization?
The receptive fields of a set of neurons organised in such a way as to reflect the spatial organisation present in the retina
What is the dorsal stream in vision? What are its two specialisations?
A pathway in vision extending from the occipital lobes to the parietal lobes
Visually guided action and attention
What is blindsight? What is a possible explanation? What causes it? Does it also cause impaired vision?
A symptom in which the patient reports not being able to consciously see stimuli in a particular region but can nevertheless perform visual discriminations accurately
Reflects the operation of other visual routes from the eye to the brain other than the V1
Damage to the V1
Yes, it does.
What is the occipital cortex outside of V1 called? Which important regions does it contain?
The extrastriate cortex
Contains regions V4 and V5/MT
What is V4?
A region of the extrastriate cortex associated with colour perception
What is V5/MT (Medial Temporal)?
A region of the extrastriate cortex associated with motion perception
What is achromatopsia? Is it the same as colour blindness? Why?
A failure to perceive colour (the world appears in grayscale)
Not the same as colour blindness since it does not involve deficient or absent types of cone cells
What is akinetopsia?
A failure to perceive visual motion
What are the four stages of object recognition?
Firstly, the recognition of basic elements such as edges, lengths, contrasts, and orientations.
Secondly, grouping based on depth cues and figure/background.
Thirdly, structural descriptions (memory representations of the three-dimensional structure of objects) are used to identify the object
Fourthly, meaning is attributed to the stimulus, with information such as its name becoming available.
What is biological motion?
The ability to detect whether a stimulus is animate or not from movement cues alone
What is colour constancy? What part of the brain ensures it?
The perception of the colour of a surface as constant even when illuminated in different lighting conditions
V4
What is associative agnosia?
A failure to understand the meaning of objects due to a deficit at the level of semantic memory.
What is figure-ground segregation?
The process of segmenting a visual display into objects versus background surfaces
What is Gestalt’s Law of Proximity?
Objects are more likely to be perceived as part of a group if they are close together
What is apperceptive agnosia?
A failure to understand the meaning of objects due to a deficit in the level of object perception
What are Gestalt’s four Principles?
Law of Proximity
Law of Similarity
Law of Continuation
Law of Closure States
law of Common Fate
What is Gestalt’s Law of Similarity?
Objects are more likely to be grouped together if they are similar
What is Gestalt’s Law of Continuation?
Edges are grouped together so that there are as few as possible interruptions
What is Gestalt’s Law of Closure States?
Missing parts of objects are filled in
What is Gestalt’s Law of Common Fate?
Elements that move together tend to be grouped together
What is the lateral occipital complex (LOC)?
A region of the brain specialised for processing object shapes
What is integrative agnosia?
A failure to integrate parts into wholes in visual perception
What is object constancy? What is the difference between viewpoint-invariant and viewpoint-dependent theories?
The ability to recognise objects from different angles and lighting
Viewpoint-invariant theories argue that particular objects or features are mapped directly to structural descriptions
Viewpoint-dependent theories argue that recognising an object involves extracting the principal axis of an object and carrying out a mental rotation into a normal viewpoint.
What is category specificity? What can this be applied to?
The notion that the brain represents different categories in different ways and/or regions
Recognition of objects
What is adaptation / repetition suppression?
A reduced neural response to a stimulus, or stimulus feature, that is repeated
Helps the brain maintain object constancy by reducing the neural response to repeated stimuli so that it can efficiently process and recognize objects without being overwhelmed by redundant information
What are face recognition units (FRUs)?
Stored knowledge of the three-dimensional structure of familiar faces
What is the parahippocampal place area (PPA) most active in recognising?
Scenes/Places
How about the extrastriate body area (EBA)?
Human bodies
What is the fusiform face area (FFA)?
An area in the inferior temporal lobe that responds more to faces than other visual objects, and is implicated in processing facial identity
What are person identity nodes (PINs)?
An abstract description of people that links together perceptual knowledge such as faces with semantic knowledge
What is the superior temporal sulcus (STS) assumed to process?
What is the superior temporal sulcus (STS) assumed to process?
What is prosopagnosia?
Impairments of face processing that do not reflect difficulties in early visual analysis
An inability to recognise previously familiar faces
What is categorical perception?
A tendency to perceive ambiguous or hybrid stimuli as either one thing or the other (rather than as both simultaneously or as a blend)
What is Farah’s model for the differences between words, objects and face recognition? What do other models state?
That they reflect different weightings of part-based versus holistic perception; faces more holistic, words more part-based, objects both
That there might be separate stores of structural knowledge for each of these categories
What does within-category discrimination refer to in the context of these models? How about “visual experts”?
That faces require within-category discrimination, while object recognition not as much.
That we become visual experts at making within-category distinctions through prolonged experience with thousands of exemplars.
