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Psychology 2015A/B Lecture Notes - Receiver Operating Characteristic, Detection Theory, Absolute Threshold

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Patrick Brown

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Psychology 2015: Sensation & Perception
Chapter 1: Introduction to Perception (Pg. 3)
- The detectors include the eyes, ears, skin receptors, and receptors in the nose
and mouth
- Perceiving occurs almost effortlessly
The Perceptual Process
- The Perceptual Process- A sequence of processes that work together to
determine our experience of and reaction to stimuli in the environment
- Process is divided into 4 categories:
o Stimulus- What is out there in the environment, what we actually pay
attention to, what stimulates our receptors
The stimulus can be in environment or within a person’s body
Environmental stimuli- All things in our environment that we
can potentially perceive
Attended stimuli- Things that are particularly focused on by the
observer; Changes from moment to moment
The attended stimulus is transformed into an image on the retina
Image is representation of stimulus
The next step involves transforming the image into
o Electricity- Electrical signals created by the receptors, which turn
energy from environment into electrical signals in the nervous system
Everything we perceive is based on electrical signals in our
nervous system
Transduction- Transformation of one form of energy into
another occurs in the nervous system when energy (light
energy, mechanical pressure, chemical energy) is transformed
into electrical energy
Transmission- Once the image is transformed into electrical
energy signals (through transduction), those signals travel from
neuron to neuron until they reach the brain
Processing- Neural processing involves interactions between
neurons, relaying the representation of the stimulus from the eye
to the brain
As electrical signals are transmitted, they undergo neural
The original electrical representation created by the receptors is
transformed by processing into a new representation of the
stimulus in the brain
o Experience & Action- Our goal is to perceive, recognize, and react to the

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Perception- Conscious sensory experience occurring when
electrical signals representing the stimulus are transformed into
an experience of observing the stimulus
Recognition- Our ability to place an object in a category that
gives it meaning
Visual Form Agnosia- An inability to recognize objects
even after perceiving the object
Action- Motor activities that occur as a result of or following
In evolution, major goal of visual processing was to help
animals control navigation; Functions for animals survival
Perception is a continuously changing process
Overall process is so dynamic and continually changing
that is doesn’t really have a beginning or ending point
Everyone can see an action but experience is personal
Experience probably leads to action
Subjective experience can’t be measured
o Knowledge- Any information we bring to the perceptual situation Can
have its effects at many different points in the process
Knowledge allows for the categorization of objects
Rat-Man Demonstration- Picture that looks like a rat and a man;
Shows how recently acquired knowledge can influence
Bottom-Up Processing (Data-Based Processes)- Processing based
on incoming data
Essential for perception b/c perceptual process begins
with stimulation of receptors
Top-Down Processing (Knowledge-Based Processing- Processing
based on previously acquired knowledge
Both types of processing often work together to create
For simple stimuli, bottom-up processing can occur on its own
When stimuli become more complex, top-down processing
Our knowledge of how things usually appear in environment can
help determine what we perceive
- Retina- 0.4mm thick network of light-sensitive receptors and other neurons
that line the back of the eye that transforms stimuli into
o Representation of attended stimuli is created on the retina
o Light energy from the representation/image is transformed into
electrical energy
How to Approach the Study of Perception
- Goal of perceptual research is to understand steps in process that lead to

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- Studied using 2 approaches: Psychophysical approach & physiological
- Psychophysical Approach- Measuring the stimulus-perception relationship.
Gustav Fechner coined the term psychophysics Referring to the measure of
relationships between stimuli and perception
- Physiological Approach- Measuring the relationship between stimulus and
physiological processes, and physiological processes and perception
o Studied by measuring electrical responses; Can also involve studying
anatomy or chemical processes
o Goal is to understand how neurons and the brain create perceptions
- Cognitive Influences on Perception- Knowledge, past experiences,
expectations, memories, and expectations that people bring to the situations
that affect how we perceive things
- To fully understand perception we need to use both approaches
Measuring Perception
- Many possible perceptual responses to a stimulus:
- Description- Indicating characteristics of a stimulus
o Phenomenological Method- Researcher asks to describe what we
perceive or to say when a particular perception occurs
First step in studying perception because it describes what we
- Recognition- Placing the stimulus in a specific category
o When categorizing a stimulus by naming it, we are measuring
- Detection- Becoming aware of a barely detectable aspect of a stimulus
o Classical Psychophysical Methods- The original methods used to
measure stimulus-perception relationship; Methods of limits,
adjustment and constant stimuli used to measure stimulus-perception
Method of Limits- Experimenter presents stimuli in ascending
(increasing intensity) or descending (decreasing intensity) order
until the person can perceive the stimulus or can’t perceive the
stimulus anymore
The change is called the crossover point
By repeating many times, starting above threshold half
the time and below the other half, experimenter can
determine threshold by getting average of all crossover
Method of Adjustment- Experimenter adjusts the stimulus
intensity continuously until the observer can just barely detect
the stimulus (fastest method)
The just barely audible intensity is the absolute threshold;
Can repeat many times and get average
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