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PS262 Study Guide - Midterm Guide: Detection Theory, Receptive Field, Occipital Lobe

Course Code
Todd Ferretti
Study Guide

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Chapter 1: Introduction to Perception
The Perceptual Process
Perception does not just happen, but it is the end result of complex “behind the
scenes” processes, many of which are not available to your awareness
The perceptual process, is a sequence of processes that work together to
determine our experience of an reaction to stimuli in the environment
The perceptual process is divided into four categories: stimulus, electricity,
experience, and action, and knowledge
The Stimulus
The stimulus exists both “out there,” in the environment, and within the person’s
Environmental stimulus is all of the things in our environment that we can
potentially perceive
The attended stimulus changes from moment to moment
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.
Is the transformation of one form of energy into another form of energy
Occurs in the nervous system when energy is in the environment—such as light
energy, mechanical pressure, or chemical energy—is transformed into
electrical energy.
After an image has been transformed into electrical signals, these signals activate
other neurons, which in turn activate other 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
Neural processing which involves interactions between neurons
Interactions between neurons is like how signals are transmitted by your cell phone
In the nervous system the signal that reaches the brain is transformed so that,
although it represents the original stimulus, it is usually very different from
the original signal
Neural processing 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

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“Backstage activity” of transduction, transmission, and processing is transformed
into things we are aware of—perceiving, recognizing, and acting on objects in
the environment
Perception is a conscious sensory experience. It occurs when your brain into your
experiences of seeing that object transforms the electrical signals that
represent an object.
Just because you see and perceive and object doesn’t mean it stops there. Other
things have happened as well, you have recognized the object, or
differentiated the object from something similar, and you take action on what
to do next after you have perceived the object. These are all still continuing
steps of perception.
Recognition is our ability to place an object in a category that gives meaning.
Although we might be tempted to group perception and recognition together, it
should be known that these are separate processes.
You can very well perceive something without recognizing exactly what it is.
Visual form agnosia—an inability to recognize objects that was caused by a brain
tumor. E.g., Dr. P who could perceive the parts of objects but couldn’t identify
the whole object.
Action includes motor activities such as moving the head or eyes and locomotion
through the environment
Some researchers see action as an important outcome of the perceptual process
because of its importance for survival.
Is any information that the perceiver brings to a situation
Information that a person brings to a situation can be things learned years ago and
can influence the perceptual process is the ability to categorize objects
Bottom-up processing is processing that is based on income data. Incoming data
always provide the starting point for perception because without incoming
data, there is no perception.
Top-down processing refers to processing that is based on knowledge.
Knowledge isn’t always involved in perception but it often is—sometimes
without our even being aware of it.
Bottom-up is essential for perception because the perceptual process usually beings
with stimulation of the receptors.
Bottom-up and top-down processing often work together to create perception
How to Approach the Study of Perception
The psychophysical approach to perception was introduced by Gustav
Fechner, who coined the term psychophysics to refer to the use of
quantitative methods to measure relationships between stimuli (physics) and
perception (psycho)
The physiological approach to perception involves measuring the relationship
between stimuli and physiological processes and between physiological

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processes and perception
The knowledge, memories, and expectations that people bring to the situation
influence their perceptions. These factors that have been described as the
starting point for top-down processing are called cognitive influences on
Measuring Perception
Description: The phenomenological method is a first step in studying perception
because it describes what we perceive. The description can be at a very basic
level, such as when we notice that we can perceive some objects as being
further away than others, or that there is a many other perceptual qualities
Recognition: when we categorize a stimulus by naming it, we are measuring
Detection: methods, limits, adjustments, and contrast stimuli are called the
classical physcophysical methods because they were the original
methods used to measure the stimulus perception relationship
The Absolute Threshold is the smallest amount of stimulus energy necessary to
detect a stimulus. For example, the smallest amount of light energy that
enables a person to just barley detect a flash of light would be the absolute
threshold for seeing that light.
The Difference Threshold is the smallest difference between two stimuli that a
person can detect.
Weber’s Research
Found that when the difference between the standard and comparison weights was
small, his observers found it difficult to detect the difference in weights, but
they easily detected larger differences
His research was stated mathematically by Fechner as DL/S=K and was called
Weber’s Law. K is a constant called the Weber Fraction.
Magnitude Estimation
If we double the intensity of a tone, does it sound twice as loud? If we double the
intensity of a light, does it look twice as bright? Although a number of
researchers, proposed equations that related perceived magnitude and
stimulus intensity, it wasn’t until 1957 that S.S Stevens developed a
technique called scaling, or magnitude estimation that accurately measure
this relationship.
As intensity is increased, perceptual magnitude increases more than intensity is
called response expansion.
The beauty of the relationships derived from magnitude estimation is that the
relationship between the intensity of a stimulus and our perception of its
magnitude follows the same general equation for each sense. These functions
are called power functions. This relationship is called Steven’s power
Threshold Measurement can be influenced by how a person chooses to respond
A way to describe the difference between two people is that each have a different
response criterion which means that everybody responses differently.
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