An Overview!

Each sensory system (sight, hearing, touch, taste, smell) is comprised of sensory cells called receptors. Perception is what happens when a person recieves information from their senses, and is conscioiusly aware of what is being sensed. For example, you might see a baseball flying at your head. This is sensing. But when you decide to move out of the way, that is percieving.

Threshold

Threshold is the line where something can or cannot be sensed. Absolute threshold is a statistically determined value that refers to a point a which a stimulus is detected 50% of the time. Difference threshold is defined as the minimum change in stimulation required for a change in detection can be noticed.

Ernst Weber (1795-1878) noticed that the stimulus for threshold changed for the intensity of the stimulus. In other words, a person carrying a one pound load would notice if you put a pound more on. However, a person carrying a 100 pound load might not. He devised a law known as Weber's Law (how creative.) Weber's Law:

The law says that the ratio of a change in stimulation to the stimulation equals a constant value.

Signal detection theory is a view that is based on a subject's ability to detect a stimulus against an environmental background of noise. Reciever operating characteristics are individual decisional factors that affect thresholds. For example, if you are waiting for your doorbell to ring, you might think that it rang, and so you go and check, but no one is there.

In a detection task where sometimes the signal occurs, and where sometimes it doesn't, the subject might want to be sure that he doesn't miss any stimuli. Therefore, he/she would be likely to over guess and have some "false alarms." This would be called a liberal observer. However, the opposite of this would be a conservative observer. This chart shows the responses of a liberal and conservative observer in an experiment with 100 trials.

This effect can be countered by rewarding correctness and punishing false alarms and misses.

Subliminal perception is perception that occurs below some threshold point where the stimulus events are not obvious. However, no strong supporting evidence shows that subliminal perception affects people in important ways.

Receptors

Sensory adaption is a loss of sensitivity that occurs at the receptor level in all sensory systems when stimuli are unchanging. Habituation is a decline in response elicited to repeated stimulation, not simply due to adaption. Ready for an analogy? Sensory adaptation is to sensing as habituation is to percieving. Wasn't that great?