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Chapter 1

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Phillip Servos

Chapter 1 – Introduction to Perception The Perceptual Process  Just as the audience sees only a small part of what is happening during a play, your perception of the world around you is only a small part of what is happening as you perceive  The perceptual process, shown in Figure 1.1., is a sequence of processes that work together to determine our experience of and reaction to stimuli in the environment  Figure 1.1 divides the processes into four categories: o Stimulus, Electricity, Experience and Action, and Knowledge  Stimulus refers to what is out there in the environment, what we actually pay attention to, and what stimulates our receptors  Electricity refers to the electrical signals that are created by the receptors and transmitted to the brain  Experience and Action refers to our goal – to perceive, recognize, and react to the stimuli  Knowledge refers to knowledge we bring to the perceptual situation  This box is located above the other three boxes because it can have its effect at many different points in the process The Stimulus  The stimulus exists both “out there”, in the environment, and within the person’s body Environmental Stimuli and Attended Stimuli  These two aspects of the stimulus are in the environment  The environmental stimulus is all of the things in our environment that we can potentially perceive  The attended stimulus is the stimulus that a person is attending to at a given point in time The Stimulus on the Receptors  This step is important because the stimulus is transformed into another form – an image on the retina  Because the item has been transformed into an image, we can describe this image as a representation of the image. Its not the actual image but it stands for the image Electricity  One of the central principles of perception is that everything we perceive is based on electrical signals in our nervous system  These electrical signals are created in the receptors, which transform energy from the environment into electrical signals in the nervous system – a process called transduction Transduction  Transduction is the transformation of one form of energy into another form of energy  Transduction occurs in the nervous system when energy in the environment – such as light energy, mechanical pressure, or chemical energy – is transformed into electrical energy Transmission  After the image has been transformed into electrical signals in the receptors, these signals activate other neurons, which in turn activate more neurons  Eventually these signals travel out of the eye and are transmitted to the brain  The transmission step is crucial because if signals don’t reach the brain, there is no perception Processing  As electrical signals are transmitted through the retina and then to the brain, they undergo neural processing, which involves interactions between neurons  The image is changed into electrical signals in the receptors, which eventually are sent out the back of the eye o This signal, which represents the image, is relayed through a series of neurons to the brain, which transforms this signal into a perception of the image  The transformation that occurs between the receptors and the brain is achieved by neural processing, which happens as the signals that originate in the receptors travel through a maze of interconnected pathways between the receptors and the brain within the brain  In the nervous system, the original electrical representation of the stimulus that is created by the receptors is transformed by processing into a new representation of the stimulus in the brain Experience and Action Perception  Perception is conscious sensory experience o It occurs when the electrical signals that represent the image are transformed by the brain into the experience of seeing the moth o Two additional steps – recognition and perception – are behaviours that are important outcomes of the perceptual process Recognition  Recognition is our ability to place an object in a category that gives it meaning  Although we might be tempted to group perception and recognition together, researchers have shown that they are separate processes  Visual form agnosia – an inability to recognize objects – that was caused by a brain tumor Action  Action includes motor activities such as moving the head or eyes and locomoting through the environment  David Milner and Melvyn Goodale (1995) propose that early in the evolution of animals the major goal of visual processing was not to create a conscious perception or “picture” of the environment, but to help the animal control navigation, catch prey, avoid obstacles, and detect predators – all crucial functions for the animals survival  The fact that perception often leads to action means that perception is a continuously changing process  The changes that occur as people perceive is the reason the steps of the perceptual process in Figure 1.1 are arranged in a circle o Although we can describe the perceptual process as a series of steps that “begin” with the environmental stimulus and “end” with perception, recognition, and action, the overall process is so dynamic and continually changing that it doesn’t really have a beginning point or an ending point Knowledge  Knowledge is any information that the perceiver brings to a situation o Knowledge is placed above the circle because it can affect a number of the steps in the perceptual process  Rat-man demonstration: the demonstration in which presentation of a “ratlike” or “manlike” picture influences an observer’s perception of a second picture, which can be interpreted either as a rat or as a man. This demonstration illustrates an effect of top-down processing on perception  An example of how knowledge acquired years ago can influence the perceptual process is the ability to categorize objects  Another way to describe the effect of information that the perceiver brings to the situation is by distinguishing between bottom-up processing and top-down processing o Bottom-up processing (also called data-based processing) is processing that is based on incoming data  Incoming data always provide the starting point for perception because without incoming data, there is no perception. o Top-down processing (also called knowledge-based processing) refers to processing that ias based on knowledge  Bottom-up processing is essential for perception because the perceptual process usually begins with stimulation of the receptors How to Approach the Study of Perception  The goal of perceptual research is to understand each of the steps in the perceptual process that lead to perception, recognition, and action  To accomplish this goal, perception has been studied using two approaches: the psychophysical approach and the psychological approach  The psychophysical approach to perception was introduced by Gustav Fechner, a physicist who, iin his book Elements of Psychophysics (1860/1966), coined the term psychophysics to refer to the use of quantitative methods to measure relationships between stimuli (physics) and perception (psycho)  An example of research using the psychophysical approach would be measuring the stimulus-perception relationship (PP) by
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