First introduced by Daniel Kahneman and Amos Tversky, the idea of cognitive bias explains something most of us have casually observed: that humans aren't always rational. The tendency to distort information coming at us from the outside world – a fluctuation in stock prices, a stranger's intentions, the likelihood that two weeks in the Bahamas will cure what ails us – happens in predictable ways based on general human cognitive tendencies and, in less predictable ways, based our individual psychological profiles.
One framework that's useful in understanding the variations in cognitive bias – why, for example, the Mona Lisa makes one person weep and another yawn – is the idea of cognitive schema (pl. schemata). Introduced by developmental psychologist Jean Piaget, a schema is our cognitive map of a concept. It's a cluster of associations that are activated when we think of a given thing. For example, when you hear the word "mom," what happens for you mentally and emotionally depends upon the sum total of your experiences with your own mother, what you've heard and read about moms real and fictional, and possibly your own experiences as a mother yourself, if you are one. For all these reasons, your reaction to a film whose theme is "motherhood" will be very different from mine or anybody else's. Perhaps you will avoid such films altogether, or be irresistibly drawn to them.
Cognitive biases and schemata can also account for what we loosely call "closed-mindedness" – the knee-jerk rejection of certain types of food, experiences, or people. Beneath our conscious, explicit justifications for such reactions ("Opera is boring") are deeper, less conscious associations ("my first girlfriend, at a time when I was desperate to impress her, told me that opera is boring.")
Cognitive schemata, while useful in helping us make sense of the world, can become rigid and distorting lenses through which we view it. Cognitive dissonance – new experiences that contradict or problematize past assumptions, can expand these schemata and enable us to see with new eyes.