Perception- depth cues, sensation vs perception and visual illusions Flashcards
What is a sensation?
A sensation is a stimulus detected in the environment and processed by sense receptors.
What is perception?
The organisation and interpretation of sensory information. It is the combination of information received by a sense receptor and the brain’s interpretation of what that information means.
What are visual cues?
Visual cues are features of our environment that give us information about movement, distance and where things are in relation to one another.
What are monocular and binocular depth cues?
Monocular: allow judgement depth and distance with one eye.
Binocular: allow judgment of depth and distance with two eyes.
State the types of monocular depth cues.
Height in plane: Objects that are higher up in the visual field appear to be further away. For example, in an image, the people that are higher up in the picture, appear to be further away in the distance.
Relative size: When objects appear smaller in the visual field than known objects of a similar size. For example, in an image, the two people in the background appear to be smaller than people at the front, showing that they’re further away.
Occlusion: Objects that are behind or obscured by other objects are further away. For example, in an image, the mountains are behind or obscured by people, showing that they’re further away.
Linear perspective: Lines that are parallel, like on a road or railway track, appear to get closer and come to a point in the distance. This shows that the point where the lines meet is further away.
State the types of binocular depth cues.
Retinal disparity: This happens because our eyes are about 6 cm apart. The amount of difference there is in the image each eye receives gives the brain information about the distance. The closer an object is the greater the difference in the two images. The further away an object is, the smaller the difference in the two images.
Convergence: if two things converge, they become closer together. The muscles around our eyes work harder when viewing objects up close. When looking at an object that is far away, the muscles are relaxed as our eyes are looking straight ahead. This muscle information provides our brain with information about the depth and distance of objects in our environment.
State the explanations for different types visual illusions. Give examples as well.
Size constancy: the brain’s ability to perceive familiar objects as the same size, despite changes in the size of the image on the retina. For example, if you see your friend at a distance, you know that it is not a tiny version of them, just that they are further away. An example of size constancy is the Muller lyer illusion. The line with the outgoing fins is perceived as longer than the line with ingoing fins because we perceive one line as closer to us.
Misinterpreted depth cues: Depth cues help us perceive distance. sometimes our brain interprets these incorrectly by interpreting distance when it is not actually there. Examples of this include the Ponzo illusion and Muller lyer illusion which fools the brain into perceiving distance because we apply size constancy when we should not. In the Ponzo illusion, converging lines in the image gives the impression of distance like a road or railway track. Our brain uses size constancy and mentally enlarges it making the top line longer than it is and longer than the line at the bottom. The line at the top is not actually long; it is just perceived as being further away.
Ambiguity: An ambiguous figure is when there are two possible interpretations of the same image, and the brain cannot decide which one to choose. An example of this is the Necker cube. The cube can be perceived as either pointing upwards to the right or downwards to the left. After 30 seconds, most people can flip between the interpretations.
Fiction: This is when a person perceives something in the image that is not actually there. The image or the stimulus may suggest a certain aspect of the figure is present, but it is not. An example of this is the Kanizsa triangle. The image suggests that there is a second triangle overlapping the first even though there is nothing there. Illusory contours create the impression that the overlapping triangle has continues edges all the way around it.
AO1 of Gibson’s direct theory of perception.
Gibson’s direct theory claims that perception happens directly. As such, perceptual abilities are innate and accurate and do not have to be learned through experience. Perception is based on current sensory information from the environment and therefore sensation and perception are the same. An example of how the brain perceives information directly is optic flow. This is where the point we are moving towards stays stationary while the rest of the view seems to rush away from it. This sensory information directly informs our brain that we are moving. Gibson identified motion parallax which is a monocular depth cue used to judge speed of movement. It refers to the fact that when we are moving objects that are closer to us appear to be moving faster than objects that are further away. Everything in our optic array provides enough information to judge depth, and distance and movement without needing to make inferences using past experience. Therefore, perception is due to nature rather than nurture.
AO3 of Gibson’s direct theory of perception.
:) - Research to support Gibson’s direct theory of perception was conducted by gibson and walk in 1960. They created a visual cliff and placed 6 month old babies on the edge, which looked like a severe drop to the baby. It was found that very few babies were crawling across the cliff to their mothers. This implies that some parts of human perception are most likely innate, as gibson’s theory suggests.
:( - one weakness of gibson’s theory is that its struggles to explain visual illusions. Gibson’s theory suggests that we will always percieve accurately without need for inference and past experiences. However, visual illusions can trick the brain into misperception. This suggests that perception is more complex than Gibson’s direct theory implies.
:) - A further strength of gibson’s theory is that it has real world application. Much of Gibson’s research that led to the development of the theory was based on the experiences of pilots from World War 2. As such, The theory can explain how everyday perception of movement and depth can occur. The real world relevance of Gibson’s directory enhances its use in explaining perception.
:( - A weakness of Gibson’s theory is that there is an alternative explanation provided by Gregory’s constructivis theory of perception. Regret theory states that perception is an active process and the information received from our senses is completed by inferences made by the brain using stored knowledge from past experiences. Therefore, Gibson’s direct theory may not be the only explanation of perception.
AO1 of Gregory’s constructivist theory of perception.
Gregory claims that perception is not direct but is an active process that involves drawing inferences. Perception is a process of construction, combining information our brain receives from our eyes with what we already know about the world. Often, the information we receive through our senses is incomplete so the brain fills the gaps using inference ( an assumption of what should be there). Stored knowledge and expectations come from past experiences (SCHEMAS) which will be individual depending on the nurturing environment.
The brain uses visual cues to help us perceive things; depth, distance, size, and shape of objects. Sometimes we interpret these cues incorrectly, for example, in the case of visual illusions. Gregory calls this the mistaken hypothesis, meaning that our brain has drawn the wrong conclusion from the available evidence.
Gregory argues that perception is learned; for example our understanding of some visual cues from our environment. it will therefore become more sophisticated the more we interact with the world. It also means that people raised in different environments and cultures might perceive things differently. This strongly suggests that perception is due to nurture not nature.
AO3 of Gregory’s constructivist theory of perception.
:) - One strength of Gregory’s constructivist theory of perception is that there is supporting research conducted by Hudson. The study demonstrated that experience affects how visual cues are interpreted. This supports the notion that perception is rooted in learning and nurture rather than nature, Suggesting that Gregory’s idea of perception being constructed is accurate.
:( - Gregory’s constructive theory of perception can be criticised for using visual illusions as evidence for perception being based on learning and inference. Visual illusions are artificial, 2 dimensional images that are designed deliberately to trick the brain. Therefore, it can be argued how daily life works and therefore it lacks real life application.
:( - Gregory’s theory of perception can be criticized further as it is unable to explain how perception starts. Research has shown that infants as young guest 6 months can perceive depth and that babies have perceptual abilities at birth. For example, they show a preference for human faces compared to random patterns. Therefore, some perception may be due to nature rather than merger contradicting Gregory’s assertion.
:( - A weakness of Gregory’s theory is that there is an alternative theory that is provided by Gibson. Gibson’s theory states that perceptual abilities are a Nate and that sensory information required is accurate and we do not need to make inferences. Therefore, Gregory theory may not be the only explanation for perception.
What are the four factors that affect perception?
Culture, motivation, emotion, expectation.
