Characteristics Of Sensory Modalities
There are two main characteristics, a psychological characteristic known as sensitivity, and a physical characteristic known as intensity.
Sensitivity
Absolute Thresholds
Sensitivity is how affected our senses are to stimuli. Stronger stimuli affect senses more (A brighter light affects your eyes more than a weak light). To start with, the absolute threshold is the minimum intensity of a stimulus needed to discriminate from no stimulus. Absolute thresholds for stimuli tend to be very small. Experimentally it is defined as when a participant can detect a stimulus 50% of the time.
Changes In Intensity
Just noticeable differences (jnds) are the minimum difference in intensity of two stimulus to tell the two apart. Ernst Heinrich Weber and Gustav Fechner found that the larger the original intensity of a stimulus, the smaller the jnd of the stimulus. Basically the jnd is proportional to the original intensity, also known as the standard. This is the Weber-Fechner law. Jnds are percentages known as Weber fractions, and they are the constant relation of the ration of standard and jnd.
Suprathreshold Sensation
Suprathreshold is conditions when stimuli are above the absolute threshold, are detectable. This is basically the sensory behavior in conditions of detectable stimuli. S. S. Stevens derived a law based on two principles: the Weber-Fechner law is correct, and that the observable differences between a constant number of jnds is constant (the observable differences of 3 and 7 jnds is the same as that of 10 and 13 jnds). This is knowns as Stevens' Law, and it states that the relationship between a response and stimulus intensity is a power function, where response is intensity raised to some power r. When r>1 this is an increasing relation, typical of senses such as pain, and when r<1 a decreasing relation, such as vision.
Signal Detection Theory
This theory is how we understand errors to occur in many situations. The way it works is when someone is trying to detect a signal against backgrounds noise, such as when you're trying to find a friend (the signal) in a crowd of strangers (the noise), you must first experience a sensation (the crowd of people as you perceive them) and this is filtered through your bias, the criterion an observer sets for making a response (your bias for waving to your friend might be seeing her green hat). Should you correctly identify your friend this would be called a hit, where a response has been generated correctly when a signal is present. Identification of a signal that is not present is a false-alarm. Different observers have different false-alarm rates. This is referred to as observer bias. Some observers are more or less prone to a claim a signal to be present.
Sensory Coding
No input to a sensory modality can be interpreted by the brain until it is in the form of an electrical signal. The process each sensory modality must undergo to translate the physical stimulus into an electrical signal to send to the brain is transduction. Then the signal is sent to the brain, and sensory coding begins. Two coded properties of a stimulus are intensity, how strong a stimulus is, and quality, what a stimulus is like. If you were to hear a musical note you would notice two properties of the note as you hear it, how loud it is, the intensity, and what note it is, the quality. Using a method called single cell recording, scientists learned howsnesory systems code intensity and quality. Intensity is coded by the frequency of neuron firings. So more intense stimulus fire more neurons every second, and the stimulus is felt more by the brain. Johannes Muller proposed in1825 that the brain codes for quality of a stimulus by the neural pathways a signal takes to the brain. So in the instance of a musical note, one frequency would take one pathway, and a higher frequency would take a slightly different one associated with that frequency.
