Activity . factors influencing learning a CR are described below: . T ime Relations between Stimuli : The classical conditioning procedures, discussed below, are basically of four types based on the time relations between the onset of conditioned stimulus (CS) and unconditioned stimulus (US). The first three are called forward conditioning procedures, and the fourth one is called backward conditioning procedure.
The basic experimental arrangements of these procedures are as follows: a) When the CS and US are presented together, it is called simultaneous conditioning . b) In delayed conditioning , the onset of CS precedes the onset of US. The CS ends before the end of the US. c) In trace conditioning , the onset and end of the CS precedes the onset of US with some time gap between the two.
d) In backward conditioning , the US precedes the onset of CS. It is now well established that delayed conditioning procedure is the most effective way of acquiring a CR. Simultaneous and trace conditioning procedures do lead to acquisition of a CR, but they require greater number of acquisition trials in comparison to the delayed conditioning procedure. It may be noted that the acquisition of response under backward conditioning procedure is very rare.
. Type of Unconditioned Stimuli : The unconditioned stimuli used in studies of classical conditioning are basically of two types, i.e. appetitive and aversive . Appetitive unconditioned stimuli automatically elicits approach responses, such as eating, drinking, caressing, etc.
These responses give satisfaction and pleasure. On the other hand, aversive US, such as noise, bitter taste, electric shock, painful injections, etc. are painful, harmful, and elicit avoidance and escape responses. It has been found that appetitive classical conditioning is slower and requires greater number of acquisition trials, but aversive classical conditioning is established in one, two or three trials depending on the intensity of the aversive US.
O PERANT /I NSTRUMENTAL C ONDITIONING This type of conditioning was first investigated by B.F. Skinner. Skinner studied occurrence of voluntary responses when an organism operates on the environment. He called them operants .
Operants are those behaviours