Infographic developed by Injury Free Nova Scotia, 2015. Used by permission.

References:

1. Schüll, N. D. (2012). Addiction by design: Machine gambling in Las Vegas. Princeton University
   Press.

The machines also use variable-ratio reinforcement strategies – the strategy that is the most powerful to condition people to keep playing. See: http://www.apacenter.com/the-problem-of-technology-addiction-part-2/

Also, since behavioural dependence activates the same dopamine reward system in the brain that addictive drugs do, use of gambling machines such as VLTs may make people more susceptible to chemical addiction. This has been established in animal studies. (e.g. see Zack, M., Featherstone, R. E., Mathewson, S., & Fletcher, P. J. (2014). Chronic exposure to a gambling-like schedule of reward predictive stimuli can promote sensitization to amphetamine in rats. Frontiers in Behavioral Neuroscience, 8, 36. doi:10.3389/fnbeh.2014.00036 for info)