Flashcards
Topic 1: Vision (Distorted)
Cards in this deck (28)
- 1What does it mean to say that vison is hierarchical? (LO4)Information is broken down to basic lower level characteristics and processed at increasing levels of complexity to build up higher level characteristics.
- 2What does it mean to say that vision is modular? (LO4)Separate modules are involved in processing different inputs (i.e. colour or motion)
"Divide and Conquer" - 3Why, in terms of visual processing in the brain, is the idea that vision is automatic and effortless a misconception? (LO4)Visual processing, whilst often occurring unconsciously, is not automatic or effortless but requires processing in and communication between multiple brain regions.
This is seen in the nature of visual processing where visual input is processed by different brain areas (vision is modular) involved in different types of processing at differing/increasing levels of complexity (vision is hierarchical) .
For example, as one progresses along the ventral stream, neurons become selective for increasingly complex stimuli – from simple oriented bars and edges in early visual area V1 to complex objects and faces in higher visual areas such as inferotemporal cortex.
Yet, whilst this is a hierarchical process, it is not serial, feedback and feedforward is occurring as well as parallel processing meaning that many different steps and analysis are occuring at the same time. - 4Why, in terms of visual input, is the idea that vision is automatic and effortless a misconception? (LO4)Input is often insufficient (due to environmental issues and physical constraints - blind spot), ambiguous, and overwhelming.
Therefore, interpretation of the visual environment is vital to enable a coherent perception of the world. This interpretation does not occur automatically or without effort. - 5Describe the initial stages of vision when light enters the eye (LO4)1. Light enters the eye through the cornea
2. The cornea and lens then refract the light rays to produce a sharply focus image on the retina
3. The iris can open and close to control the amount of light that reaches the retina.
4. The retina is made up of three layers; rod and cones (photoreceptors), bipolar cells and ganglion cells. - 6Decribe the progression of visual input after light hits the eye (LO4)1. Photoreceptors stimulate the bipolar cell which in turn stimulate the ganglion cells which form the axons of the optic nerve.
2. The optic nerve conducts visual input to the dorsal lateral geniculate nucleus (LGN) in the brain which then, via optic radiations, transmits the input to the primary visual cortex (striate cortex).
3. From here visual input is passed onto other brain regions involved in processing different types of inputs. - 7Describe the role of rods (LO4)Both rods and cones are photoreceptors, however;
- Rods are sensitive to very low levels of light so are important when we are moving in semi darkness or trying to view a relatively dim stimulus.
- They can distinguish different light intensities so contribute to our perception of brightness but are not sensitive to colour differences. - 8Describe the role of cones (LO4)Both rods and cones are photoreceptors, however;
- Cones are sensitive to colour differences so detect different wavelengths
-However, require a lot of light to work and are found primarily in the fovea.
- Cones also enable you to discern fine detail, in other words they enable acuity. - 9Why is the idea that we recieve input across the whole visual field a misconception? (LO4)The majority of cones are found at the fovea in the centre of the eye, which is why you point your eyes towards a target when you want to see detail.
Due to this we can only see colour and detail for visual input falling on to the fovea or, in other words, we only can only see detail and colour for items we fixate on.
Therefore, in terms of detail and colour, we do not receive input across the whole visual field. - 10How do we construct an apparently rich and continiuous perception of the envrionment given the gaps in the input we recieve? (LO4)Yet, we perceive our environments to be continuous and detailed.
Saccades are rapid jerky movements of the eye and they allow us to scan a visual scene, fixating on areas of interest, to build up an image of it. - 11What does change blindness indicate? (LO4 - relating to misconception 2)Changes in our environments represent important visual information as we may have to adapt to them.
Yet, despite saccades allowing us to scan a visual scene and fixate on areas of interest, we are sometimes blind to these changes.
When distract by flicker in an image, it has been shown that we usually do not, at least until we are told to look for a difference,
detect changes (e.g in colour or orientation of objects) in an image.
This demonstrates that our visual system is not, and cannot be, sensitive to all the input from our environments all of the time. Moreover, it indicates that our eyes are not building up a veridical image of a scene. - 12Why is the idea that vision sends an exact copy of what is in front of you to your brain a misconception? (LO4)Visual input is often ambiguous, insufficient, and overwhelming.
Therefore, interpretation of this input is necessary to build up a coherent and consistent perception of our visual environments.
This interpretation and analysis of visual input begins before the information reaches the brain, so the information the brain receives is not merely a copy of what is in front of you.
The optic nerve is responsible for conducting visual signals from the retina to the brain. However, cells in the optic nerve also engage in analysing visual input before it reaches the brain. - 13What process demonstrates that vision does not send an exact copy of what is in front of you to the brain? (LO4)An example of this is lateral inhibition.
This where the stimulation of particular cells, in the optic nerve, inhibits the activity of neighbouring cells.
One consequence of this is that cells detecting the edge of a surface are less inhibited compared to those detecting the middle of a surface. This results in the exaggeration of contrast at the edge of an object (edge enhancement). - 14Why is edge enhancement important and what does it demonstrate? (LO4)Edge enhancement is important because, by highlighting the edges of an object, it defines an objects shape which is crucial in allowing us to find out what an object is.
But, in exaggerating the input relating to the edge of an object, visual processing at this early stage is not just replicating the input.
Instead, interpretation and analysis of the input is occurring showing that the information send from the retina to brain is not an exact copy of what is in front of us. - 15What is the dorsal stream and where does it run from and to? (LO2)The dorsal (or the "where") stream runs from the primary visual cortex in the occipital lobe forward into the parietal lobe.
Seems to be involved in spatial awareness, in terms of guiding our actions based on our perception of where an object is. - 16What can damage to the dorsal stream result in? (LO2)Damage to dorsal stream (in particular the posterior parietal cortex) can result in optic ataxia.
This where patients appear to be unable to use visuospatial information to guide arm movements.
For example, patients with this condition can usually verbally recognise or identity objects and where they are but appear to have great difficulty co-ordinating movements to reach for them when asked to. - 17What is the ventral stream and where does it run from and to? (LO2)The ventral (or the "what") stream is associated with recognition of forms, shapes and categories of objects.
It runs from the primary visual cortex downward to the temporal lobe. - 18What can damage to the ventral stream result in? (LO2)Damage to ventral stream (usually posterior temporal lobe) can result in visual agnosia.
This can be described as a "failure to know" where people with this condition cannot identify objects by sight.
This seems to be a specific deficit in recognition as these patients typically show no impairments in memory and language skills necessary to produce the word identifying an object. - 19In what way is visual input often insuffient?(LO1/3)The nature of our environments can mean that visual input is often insufficient by itself to build a coherent perception of scene. For example, there may be objects obscuring what we are looking at or the lighting may be poor.
Equally, constraints of our visual system also results in visual input being insufficient. For example, we can only see colour and detail on objects that fall onto on our fovea. We also have a blind spot. - 20In what way is visual input often ambigous? (LO1/3)Visual input is often ambiguous in sense that input could represent many things. For example, the basic visual input you receive looking at objects may be very similar so working out what the input is likely to represent is a challenge for the visual system.
- 21What is the binding problem? (LO1/3)Moreover, it seems that many respects visual processing is modular in the sense that different regions seem to be involved in processing different features of visual input.
So this presents a challenge for the visual system in terms of how information processed in different brain regions is integrated to produce the consistent and whole visual perception we experience. - 22What are illusory contours and why do we percieve them? (LO1/3)Illusory contours (e.g the kanizsa triangle) are where we perceive an edge to present in an despite no explicit lines or colour/brightness change across the edge . Instead the physical configuration of the image seems to induce the perception of the edge.
We appear to perceive these illusions due to our visual processing systems in the brain over interpreting the images.
Gestalt psychologists argue that this occurs due to the law of closure: a bias our visual system has in towards perceiving closed figures rather than wholes ones. - 23How did the brain evolve to see the world? (LO3)"Not see the world as it is but to see the world in a way that's useful"
From Beau Lotto Ted Talk - 24In terms of neural stimulation how might visual input be ambiguous? (LO4/3)At neural level different objects may elicit the same pattern of activity.
- 25In summary why do we perceive visual illusions? (LO1)A challenge of the visual system's is in interpreting often ambigious, insufficient, and overwhelming information in order to provide a constant and consistent perception of the world.
In doing this, our perceptual systems can sometimes misinterpret information and it is this that underpins our perception of visual illusions. - 26What is one way the visual system attempts to deal with ambiguous or insufficient (e.g missing) information? (LO1)By using the context (e.g the nature of surrounding objects, what is going on in a situation, and our knowledge of how it might proceed) a visual scene to provide an estimates of what the most probable interpretation is.
This is demonstrated in cases of perceptual 'filling in' such as when visual information falls on the blind spot but also in illusions such as Ebbinghaus illusion. This where the size of a circle is perceived differently, despite its size remaining constant, depending on sizes of the circles surrounding it. - 27How has it been suggested that the visual system uses context in building perception? (LO1)Gregory (1970) suggests that this occurs via top down processes based on heuristic 'best guesses'. Factors that likely contribute to these guesses are prior knowledge about a situation and also Gestalt principles
For example, Carbon (2014) discusses how people's perception of bistable images can be influenced by information primed before seeing the images. Additionally, some cultural variation in perception of visual illusions has been found which has been argued as evidence of different past experiences and expectations influencing perception. (e.g Segal et al, 1967- perception of Mueller-Lyer illusions).
Gestalt principles appear to be assumptions the visual processing system makes in combining information. (For example...) Therefore, when there is ambiguous information these principles may guide the system in interpretation. - 28How have bottom up processes be implicated in the interpretation of ambiguous stimuli? (LO1)The role of lateral inhibition in contrast effects and brightness illusions.
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- Distorted Worlds Flashcards on Topic 1: Vision (Distorted) , created by Nichola Livermore on 11/04/2017.
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- Nichola Livermore · Apr 2017
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- Aug 4, 2017
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