Hello. So folks in psychology of learning I thought I’d make a brief video to talk a little about overshadowing versus blocking In classical conditioning this is chapter 7 so remember in the phenomenon of overshadowing you start presenting a compound stimulus that's two stimuli being presented simultaneously before the unconditioned stimulus right so overshadowing starts with a compound stimulus being presented two stimuli being presented simultaneously the thing is one of those two stimuli is more Salient or stronger than the other stimulus and it is that more Salient or stronger stimulus that is going to become classically conditioned the weaker of the two stimuli will not be classically conditioned so we explained this or one possible explanation for overshadowing is the information value explanation for classical conditioning so if the conditioned stimulus is providing useful information to the organism then classical conditioning will happen you have one weak stimulus and one strong stimulus both being presented simultaneously before the unconditioned stimulus but one of those is stronger right and so the stronger stimulus is providing the argument goes more useful information to the organism and so it is that stronger stimulus that becomes classically conditioned in overshadowing that is overshadowing next we have the phenomenon of blocking in blocking In classical conditioning remember that one stimulus one neutral stimulus by itself is paired with the unconditioned stimulus first so you pair that neutral stimulus with the unconditioned stimulus for a while then you add a second neutral stimulus to the first creating a compound stimulus you present both those stimuli simultaneously now for a while before the unconditioned stimulus then you test those two what were neutral stimuli individually which one becomes classically conditioned it is the first neutral stimulus that was paired by itself with the unconditioned stimulus that becomes conditioned right the one that you add later on does not become conditioned and remember we got competing explanations for the phenomenon of blocking so once again you have the information value of the conditioned stimulus or information value explanation for it the first stimulus was paired with the unconditioned stimulus first so it is already providing useful information to the organism by the time you add a second stimulus to that situation that second stimulus provides no new information and so is not conditioned correct a second possible explanation for the phenomenon of blocking came from Rescorla-Wagner theory where we said Rescorla-Wagner the amount of learning possible in any learning situation represented by the Greek letter theory proposes that there is a maximum amount of learning possible in any learning situation represented by the Greek letter Lambda and so when you present the first stimulus with the unconditioned stimulus what happens is that first stimulus uses up all of that Lambda or possible learning that can happen so by the time you add the second stimulus to the situation in blocking all the learning has been used up and no more learning can happen so those are two of the explanations for blocking remember there are four total