 Sensory systems enable organisms to obtain necessary information for survival  Example: a frog has eyes with receptors that are designed to detect the movement of small black shapes, but a frog would starve to death if it were knee-deep in motionless flies  Example: the human ear is designed to be most receptive to a baby’s cry  We are constantly bombarded with all kinds of stimuli, some of which we are highly sensitive to, many of which we are completely unable to detect  Ultra low or high frequency sound waves (elephants)

 Absolute threshold: minimum stimulation necessary to detect a particular stimulus  Light, sound, pressure, taste, odor  Stimulus below the absolute threshold can not be detected  E.g. ultraviolet light  We measure absolute threshold by recording the stimulation necessary for someone to pinpoint its appearance 50% of the time.

 Absolute Threshold Absolute Threshold

Subliminal

 Subliminal Stimuli = below one’s absolute threshold for conscious awareness  It was once believed that advertisers would manipulate consumers by flashing messages for incredibly brief moments of time during movies and television  Are we able to detect these subliminal stimuli?  Can subliminal stimuli still impact us?

 Remember: the absolute threshold represents the amount of stimulation for us to detect a stimuli 50% of the time  Therefore, below this threshold we are still able to detect stimuli SOME of the time  Research has shown that subliminal stimuli can actually impact us  Rating images of people  Priming us to respond later

 As well as being able to detect the presence of a minute stimuli, we must also be able to detect small differences as a stimuli changes  Difference threshold = the minimum difference a person can detect between any two stimuli  Just Noticeable Difference (JND)  The JND is not a constant, fixed value  Depends upon the magnitude of the stimulus

 Example:  If you add 10g to a 100g weight and you WILL notice the difference  If you add 10g to a 100kg weight, and you will NOT notice the difference ▪ The change in stimulus was constant, but the different threshold was increased because of the increased magnitude of the stimulus  When the magnitude increases, the value of the JND also increases

 Weber’s Law = to perceive a difference in stimuli, they must differ by a constant percentage (not amount).  Different for each type of sensory information  Light = 8%  Weight (pressure) = 2%  Sound = 0.3%

Class Question:  Imagine you are in charge of designing a new coin system for Ghana.  Why would it be useful to apply the principles of the JND in your design?  Think of an example from your own activities today that demonstrates sensory adaptation for light, sound, and pressure.

 When a stimulus is presented constantly, we become insensitive to it  Example: Move your watch up an inch on your wrist, and you will notice it for only a few minutes  Sensory adaptation = our diminished sensitivity to unchanging stimulus  What about vision?

 Sensory Adaptation for taste

 Remember: Psychology is a science  Design a procedure to determine the JND for either light, sound, smell, taste, or pressure.