Lecture: Sensation and Perception
Reading Assignment 8:
Basic Principles... (pp. 100-109)
Click for Objectives for Reading Assignment 8

The eighth reading assignment introduces concepts associated with a sub discipline of Psychology referred to as Psychophysics. Many of the earliest methodologies and research findings of Psychophysics must be attributed to the work of Gustav Theodor Fechner (http://en.wikipedia.org/wiki/Psychophysics); one of his findings will be discussed later (See Fechner’s Law).

In addition to the definition shared here, Psychophysics can loosely be explained as the study of the relationship between Sensation and Perception. Sensation is essentially a biological response to energy that is detectable in our immediate environment. Perception, however, is the psychological experience or interpretation of that energy. The latter is responsible for why two individuals sitting right next to each other can stare at the same sunset and have very different experiences. One person, Person A, might perceive the sunset as one of the most beautiful and breathe taking scenes that he/she has ever experienced. While the other person, Person B, might like little to nothing about the same sunset. Both Person A and Person B have arguably experienced the same process of Transduction, which permitted them both to see the sunset as it appears. However, the Perception of that event is very different for each of them.

The biological process of Sensation begins with the Sensory Receptor. To minimize confusion, the Sensory Receptor is nothing more than a Neuron. It has been stated before that neurons are named and distinguished based on their function and location. The neurons that are located in the body that function as the first point of contact with environmental energy, are suited for the five Senses. They are called Sensory Receptors.

As stated by Kowalski and Westen (2009), there are certain common features that all of the senses share: First, they must translate physical stimulation into sensory signals. Second, they all have thresholds below, which is when a person does not sense anything despite external stimulation. Third, sensation requires constant decision making. The decision making occurs every time an individual tries to distinguish meaningful from irrelevant stimulation. Fourth, sensing the world requires the ability to detect changes in stimulation, for example, when a person notices when a bag of groceries has gotten heavier or a light has dimmed. Fifth and finally, efficient sensory processing means "turning down the volume" on information that is redundant; the nervous system tunes out messages that continue without change.

Depending on the particular sense in question, Sensory Receptors may be located throughout the (1) eye, (2) nose, (3) ear, in the (4) tongue, or the (5) skin. The Brain has several techniques that assist in how intensity and quality are coded and distinguished by Neurons. For instance, the intensity of a sensation is discriminated by the number of sensory neurons that fire, their frequency of firing, or some combination of the two. With respect to quality, it typically is discriminated by the type of receptors involved and the pattern of neural impulses (Kowalski & Westen, 2009).

Contributions of Psychophysics
This discipline of Psychophysics has made many contributions since its establishment in the late 1890’s. For example, the notion of Sensory Adaptation explains why foul smells, loud noises, and glaring lights are more tolerable as time passes. The process of Transduction only occurs when an environmental stimulus distributes enough energy to surpass an individual’s Absolute Threshold for that particular sense. Detecting a stimulus is just the beginning. As many researchers have investigated the concept of Difference Thresholds and have established the Just Noticeable Differences (JND) at a variety of stimulus intensities, paying close attention to the relationships between sensation and perception across varying intensities has resulted in the discovery of several laws, such as the Fechner’s Law, Weber’s Law, and Stephens’ Power Law , to name a few.



A. Lefton, L.A. & Brannon, L. (2003). Psychology (8th Ed.). Allyn & Bacon: Pearson Education, Inc.

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