The terms are often used interchangeably, but confounding are actually a type of extraneous variable. Extraneous variables are all those other variables that might be part of a study, apart from the independent and dependent variables. Extraneous variables MUST be dealt with since they can harm your ability to state that the independent variable was the sole influence on the dependent variable. While you can manipulate them as independent variables, you may also have to control for them when they are not one of the variables specifically being investigated. Any influence they may have on the dependent variable may cloud the effects of the independent variable, the one you are really interested in studying.
Experimenters are also a source of extraneous variables.
Less obvious experimenter variables, such as expectancies and personal biases can be extremely damaging. A lift of an eyebrow, a slight smile, a quizzical look may be noticed by a subject and affect the way the subject acts, thus influencing the dependent variable. Methods to address the problem of extraneous experimenter variables will be discussed in later lectures. Situational variables are those that are particular to the context in which the study is being conducted. Such things as temperature, time of day, noise, lighting etc are characteristics of the situation.