Learning theory explains gambling in terms of operant conditioning: gambling behaviour is reinforced and this increases the likelihood that the behaviour will be repeated. Griffiths (2009) argues that some types of gambling, such as slot machines, may become addictive because, as well as financial rewards, there are physiological rewards (the adrenaline and dopamine ‘buzz’ of winning’), psychological rewards (excitement) and social rewards (praise from peers). Many gamblers talk about having a large win or winning streak early in their gambling career and Aasvad (2013) found that they continue to gamble in order to repeat these early experiences. Gambling is reinforced on a partial schedule (not every time), which makes it resistant to extinction. Gambling machines pay out on a variable reinforcement schedule, which is a type of partial reinforcement where only a proportion of responses are reinforced and there is no fixed pattern; this lack of predictability keeps people gambling.