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Chapter 1

PS262 Chapter Notes - Chapter 1: Gustav Fechner, Psychophysics, Action Action

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Phillip Servos

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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
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 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
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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
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 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 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 includes motor activities such as moving the head or eyes and locomoting through the
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
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