Sensation Dr.Naif AlMutawa Date 27/1/2013

1. Chapter 4
Sensory Processes
Use with Atkinson & Hilgard’s Introduction to Psychology 15th edition
Nolen-Hoeksema, Fredrickson, Loftus, Wagenaar
ISBN 9781844807284 © 2009 Cengage Learning

2. Sensory Processes
• Senses:
– Include vision, hearing, smell, taste, and touch (which
includes pressure, temperature and pain)
• Sensation
– At psychological level, sensations are raw
experiences of stimuli not yet imbued with meaning
Use with Atkinson & Hilgard’s Introduction to Psychology 15th edition
Nolen-Hoeksema, Fredrickson, Loftus, Wagenaar
ISBN 9781844807284 © 2009 Cengage Learning

3. Characteristics of Sensory Modalities
• Sensory system
– Task of acquiring information from environment and
transducing it into neural representation in brain
• Threshold sensitivity
– Absolute thresholds: detecting minimum intensities
• The absolute threshold is the minimum amount of stimulus
which reliably registers on sensory organ
• Values determined using psychophysical procedures –
measure relation between physical magnitude of some
stimulus (e.g. the physical intensity of the light) and
psychological response (how bright the light appears to be).
It’s the value the stimulus at which it is detected 50% of time.
Use with Atkinson & Hilgard’s Introduction to Psychology 15th edition
Nolen-Hoeksema, Fredrickson, Loftus, Wagenaar
ISBN 9781844807284 © 2009 Cengage Learning

4. Psychophysical procedures
In one commonly used technique, the
experimenter first selects a set of stimuli
whose magnitudes vary around the
threshold. Over a series of what are called
trials, the stimuli are presented one at a time
in a random order and the observer is
instructed to say yes if the stimuli is present
and no if it is not. Each stimulus is
presented many times for a percentage of
yes. Use with Atkinson & Hilgard’s Introduction to Psychology 15th edition
Nolen-Hoeksema, Fredrickson, Loftus, Wagenaar
ISBN 9781844807284 © 2009 Cengage Learning

5. Characteristics of Sensory Modalities
• ...Threshold sensitivity
– Difference thresholds: detecting change in intensity
• Difference threshold is the minimum difference between two
stimuli which can be reliably distinguished by sensory organ
• Another term is the JND or the Just Noticeable Difference
• In a typical change detection study, observers are presented
with a pair of stimuli. One is the standard that all is compared
to. The other is called a comparison stimuli. The observers
are asked to respond with “more” or “less” than the standard.
Use with Atkinson & Hilgard’s Introduction to Psychology 15th edition
Nolen-Hoeksema, Fredrickson, Loftus, Wagenaar
ISBN 9781844807284 © 2009 Cengage Learning

6. Characteristics of Sensory Modalities
• ...Threshold sensitivity
– Heinrich Weber and Gustav Fechner found that the larger the
value of the standard stimulus, the less sensitive the sensory
system is to changes in intensity. In fact, the intensity by which
the standard must be increased is proportional to the intensity of
the standard.
Use with Atkinson & Hilgard’s Introduction to Psychology 15th edition
Nolen-Hoeksema, Fredrickson, Loftus, Wagenaar
ISBN 9781844807284 © 2009 Cengage Learning

7. Characteristics of Sensory Modalities
• Signal detection theory
– Information consists of signals and noise where
“signal” refers to important aspect of information and
“noise” refers to unimportant aspect of information
Use with Atkinson & Hilgard’s Introduction to Psychology 15th edition
Nolen-Hoeksema, Fredrickson, Loftus, Wagenaar
ISBN 9781844807284 © 2009 Cengage Learning

8. Characteristics of Sensory Modalities
• ...Signal detection theory
– Hits and false alarms
• False alarm – signal falsely detected where there is only noise
• Hit – signal correctly detected
• Sensitivity of sensory organ indicated by differences in hits
and false alarms
– Sensitivity and bias
• Useful characteristic of signal detection analysis – allows
process of detecting stimulus to be separated into two
numbers – one representing sensitivity to signal and one
representing bias in stating “signal present”
Use with Atkinson & Hilgard’s Introduction to Psychology 15th edition
Nolen-Hoeksema, Fredrickson, Loftus, Wagenaar
ISBN 9781844807284 © 2009 Cengage Learning

9. Characteristics of Sensory Modalities
• Sensory coding
– Two fundamental issues for sensory systems
• How to translate incoming physical information and how to
encode aspects of physical information to corresponding
neural representation
• Specialized cells called receptors (specialized neurons)
detect stimulus (are activated) and pass an electrical signal
to connecting neurons through to cortex where the electrical
signal results in conscious sensory experience
Use with Atkinson & Hilgard’s Introduction to Psychology 15th edition
Nolen-Hoeksema, Fredrickson, Loftus, Wagenaar
ISBN 9781844807284 © 2009 Cengage Learning

10. Characteristics of Sensory Modalities
• ...Sensory coding
– Coding of intensity and quality
• Useful sensory information includes intensity and quality of
stimulus
• Primary means for coding intensity of stimulus is via the rate
of neural impulses – greater intensity, greater firing rate and
greater firing rate, greater perceived magnitude of stimulus
• Coding quality is more complex. It is generally agreed that
the brain codes qualitative differences between sensory
modalities according to the specific neural pathways
involved. Sensory system may also use a pattern of neural
firing to code quality of sensation
Use with Atkinson & Hilgard’s Introduction to Psychology 15th edition
Nolen-Hoeksema, Fredrickson, Loftus, Wagenaar
ISBN 9781844807284 © 2009 Cengage Learning