Understanding Psychology (10th Ed)

M O D U L E 1 0 
 
Sensing the World Around Us
Study Alert
Remember that 
sensation
refers to the activation 
of the sense organs 
(a physical response), 
whereas 
perception
refers to how stimuli are interpreted 
(a psychological response).
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100 Chapter 
4 
Sensation and Perception
Absolute Thresholds: 
Detecting What’s Out There
Just when does a stimulus become strong enough to be detected by our sense organs? 
The answer to this question requires an understanding of the concept of absolute 
threshold. An
 absolute threshold 
is the smallest intensity of a stimulus that must be 
present for it to be detected (Aazh & Moore, 2007).

Despite the “absolute” in absolute threshold, things are not so cut and dried. As 

the strength of a stimulus increases, the likelihood that it will be detected increases 
gradually. Technically, then, an absolute threshold is the stimulus intensity that is 
detected 50% of the time. 
It often takes a very small stimulus to produce a response in our senses. For 
example, the sense of touch is so sensitive that we can feel a bee’s wing falling on our 
cheeks when it is dropped from a distance of 1 centimeter. Test your knowledge of the 
absolute thresholds of other senses by completing the questionnaire in Figure 1. 
In fact, our senses are so fi ne-tuned that we might have problems if they were 
any more sensitive. For instance, if our ears were slightly more acute, we would be 
able to hear the sound of air molecules in our ears knocking into the eardrum—a 
phenomenon that would surely prove distracting and might even prevent us from 
hearing sounds outside our bodies. 
Of course, the absolute thresholds we have been discussing are measured under 
ideal conditions. Normally our senses cannot detect stimulation quite as well because 
of the presence of noise. Noise , as defi ned by psychophysicists, is background stimu-
lation that interferes with the perception of other stimuli. Hence, noise refers not just 
to auditory stimuli, as the word suggests, but also to unwanted stimuli that interfere 
with other senses. 
For example, picture a talkative group of people crammed into a small, crowded, 
smoke-fi lled room at a party. The din of the crowd makes it hard to hear individual 
voices, and the smoke makes it diffi cult to see, or even taste, the food. In this case, 
the smoke and the crowded conditions would both be considered “noise,” because