Perception Models in Psychology: Understanding How We Interpret the World
A particular problem for psychologists is explaining how the physical energy received by sense organs forms the basis of perceptual experience. To understand this complex process, various perception models have been developed, each offering unique insights into how we interpret the world around us.
Optical illusions demonstrate how our perception can be influenced by context and prior knowledge.
Bottom-Up vs. Top-Down Processing
Perception can be broadly categorized into two types of processing: bottom-up and top-down. Bottom-up processing is also known as data-driven processing because perception begins with the stimulus itself.
Stimulus information from our environment is frequently ambiguous, so to interpret it, we require higher cognitive information either from past experiences or stored knowledge in order to make inferences about what we perceive. Top-down processing refers to the use of contextual information in pattern recognition. For example, understanding difficult handwriting is easier when reading complete sentences than reading single and isolated words.
Gregory's Constructivist Theory of Perception
Richard Gregory proposed a constructivist theory of perception, emphasizing the role of prior knowledge and hypotheses in shaping our perceptual experiences. For Gregory, perception is a hypothesis which is based on prior knowledge. Therefore, the brain has to guess what a person sees based on past experiences. Highly unlikely objects tend to be mistaken for likely objects. Gregory has demonstrated this with a hollow mask of a face.
The Necker cube is a good example of this. When the perception changes though there is no change in the sensory input, the change of appearance cannot be due to bottom-up processing.
The Necker cube illustrates how our brain can interpret the same visual input in multiple ways.
For example, we respond to certain objects as though they are doors, even though we can only see a long narrow rectangle as the door is ajar.
Hypothesis Testing in Perception
Gregory's theory raises important questions about the nature of perceptual hypotheses. If perceptions make use of hypothesis testing, the question can be asked, “what kind of hypotheses are they?” Scientists modify a hypothesis according to the support they find for it, so are we, as perceivers, also able to modify our hypotheses? One would expect that the knowledge we have learned (from, say, touching the face and confirming that it is not “normal”) would modify our hypotheses in an adaptive manner.
Consider the following example: This probably looks like a random arrangement of black shapes. In fact, there is a hidden face in there; can you see it? Once the face is discovered, very rapid perceptual learning takes place and the ambiguous picture now obviously contains a face each time we look at it.
Can you find the hidden face?
Constructivists like Gregory frequently use the example of size constancy to support their explanations. That is, we correctly perceive the size of an object even though the retinal image of an object shrinks as the object recedes. However, in the real world, retinal images are rarely seen in isolation (as is possible in the laboratory). There is a rich array of sensory information, including other objects, background, the distant horizon, and movement. This is crucial because Gregory accepts that misperceptions are the exception rather than the norm.
Gibson's Direct Perception Theory
James Gibson (1966) argues that perception is direct and not subject to hypothesis testing, as Gregory proposed. Gibson’s bottom-up theory suggests that perception involves innate mechanisms forged by evolution and that no learning is required. The optic array contains invariant information that remains constant as the observer moves. This optic array provides unambiguous information about the layout of objects in space. Because of movement and different intensities of light shining in different directions, it is an ever-changing source of sensory information. Changes in the flow of the optic array contain important information about what type of movement is taking place. If the flow appears to be coming from the point, it means you are moving towards it.
Invariants are aspects of the environment that don’t change. Another invariant is the horizon-ratio relation. Affordances are, in short, cues in the environment that aid perception.
Gibson identified several key factors that contribute to our perception of the environment:
- TEXTURE GRADIENT: The grain of texture gets smaller as the object recedes.
- RELATIVE SIZE: When an object moves further away from the eye, the image gets smaller.
Gibson’s emphasis on DIRECT perception provides an explanation for the (generally) fast and accurate perception of the environment. It’s an excellent explanation for perception when viewing conditions are clear.
Criticisms of Gibson's Theory
Despite its strengths, Gibson's theory faces several criticisms. There is strong evidence to show that the brain and long-term memory can influence perception. Gibson’s theory also only supports one side of the nature-nurture debate, that being the nature side. Neither can Gibson’s theory explain naturally occurring illusions. Gibson’s theory appears to be based on perceivers operating under ideal viewing conditions, where stimulus information is plentiful and is available for a suitable length of time.
The Interplay of Nature and Nurture
A substantial body of evidence has been accrued favoring the nativist approach.
Research by Tulving et al. manipulated both the clarity of the stimulus input and the impact of the perceptual context in a word identification task.