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Chapter 1

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McGill University
PSYC 212
Jelena Ristic

Chapter One Principles of Perceptual Measurement Chapter Outline The first chapter in most academic textbooks forms the foundation for material to be presented in later chapters and The Fundamentals of Sensory Perception is not different in this respect. Much of what you learn in this chapter will be applied to specific sensory systems in later chapters. In this chapter, you will come to appreciate the various psychophysical methods that have been developed and how they are used to understand our sensory perceptual systems. As such, the focus in this chapter is on gaining an understanding of the basic relationship between our perceptual experience and the physical stimulus that acts upon a sensory system to produce the perception. You will learn about classical methods of psychophysics, including the methods of adjustment, limits, and contant stimuli, highlighting the work of Fechner and Weber. Weber’s law deals with how much additional stimulus intensity is needed for a subject to just notice a difference in the stimulus intensity. For example, if you had 10 pennies in each hand, how many more pennies would you need to add to your left hand before the weight of the pennies was noticably more than the weight of the 10 pennies in your right hand. Modern methods of psychophysics are introduced with the work of Stanley Stevens. In this context you learn of magnitude estimation in which a direct rating is provided by a subject based on his or her sensory experience. This led Stevens to develop the power law, which relates sensory experience to the intensity of a stimulus raised to a certain power and the value of this power depends on the actual sensory input. You will also learn that some sensory experiences can be directly linked to stimulus intensity and these are known as prothetic sensations whereas others, known as metathetic sensations, cannot be directly linked. The final part of the chapter examines signal detection theory. This procedural advancement in psychophysics allows researchers to determine the sensitivity of an individual to a particular stimulus by examining experimental trials when the stimulus is present for detection and when it is not present for detection, which was not done with the early methods of psychophysics because the stimulus was always present on each trial. Learning Objectives This chapter will help you 2  develop a timeline of the key researchers and their contributions to the field of psychophysics and the study of sensory perception.  understand how researchers quantify the subjective experience of sensory perception using difference and absolute thresholds and relate each to examples found in the environment.  draw and use psychometric functions as a means of understanding the relationship between psychophysical variables and to distinguish between different measures.  use examples to differentiate between the different experimental methods used in sensory perception research and to understand the advantages and disadvantages of each method.  apply psychophysical equations of magnitude estimation and scaling to calculate detection thresholds.  understand that not all sensory experiences can be quantified using the same principles or laws. You will learn to identify prothetic and metathetic sensory experiences and learn the scaling techniques used for each.  consider the human factors that influence our perception of stimuli in our environment and understand how these factors can affect how we respond to our environment. You will also learn to apply this knowledge to develop strategies in guiding your own life and behaviour. Study Questions True/False Indicate whether the statement is true or false. ____ 1. There is one Weber fraction that applies to all sensory systems. ____ 2. A standard stimulus is known as a modulus. 3 ____ 3. When using Stevens method of estimation, the subject is able to develop their own modulus. ____ 4. The difference threshold is also known as the just noticeable difference. ____ 5. Like William James, Stanley Stevens believed that sensations cannot be measured. ____ 6. Multi-dimensional scaling is only used in the study of sensation and perception. ____ 7. In signal detection theory, the concept of noise can include things that are internal and external to the perceiver. ____ 8. Sensation arises from perception. Multiple Choice Identify the choice that best completes the statement or answers the question. 1. The relation between the perceived magnitude of a stimulus and the physical intensity of that stimulus is known as a _______________. a) logarithmic function b) cross-modal comparison c) function d) psychophysics 2. The slope of a linear function _______________. a) decreases over its entire range b) remains constant c) progressively increases d) a linear function has no slope 3. The field of psychophysics was established in 1860 by _______________. a) Weber
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