Sensory information, via our eyes, ears, and other organs, forms the foundation of our lived experience. Yet we find ourselves perceiving the world differently from our family, friends, and the person sitting next to us at our favorite sports event, who calls the ball out when it clearly hit the line! So how accurate is our perception, really? This isn’t just an intellectual question about the physiological and psychological processes happening throughout our body; it has real world consequences.
Perception involves converting sensory information, such as chemical processes or air pressure, from across our body into something interpretable and meaningful. For example, the conversion of light waves that hit the retina in our eyes into the experience of sight.
However, this paints only part of the picture. Perception is in part constructed by our brain! Meaning what you see, hear, or feel is a combination of sensory information from your sensory organs (bottom-up processes) AND your brain’s prediction or what it expects to experience (top-down processes). Together, these bottom-up and top-down processes shape our perception of the world! The impact of top-down processes on our perception has critical implications: from the accuracy of human testimony to the types of treatments we offer in healthcare (e.g., cognitive-behavioral therapy for pain). In this blog we will explore evidence of constructed perception, and why it’s an adaptive process.
Visual illusions
Examine the two tiles below, labeled “A” and “B”. They are the same color, right?
Now pay attention to the color of the tiles as the full image is slowly constructed.
In the final image, we perceive the two tiles as different colors, despite our computer’s pixels displaying the same color value for both. The perceived lightening of tile B is a story told by our brains, drawing from our prior experience with checkerboard patterns and shadows. Despite being consciously aware the tiles share the same color; we can’t override this “wrong” perception.
What does this tell us about perception? Visual illusions, such as this one, offer evidence that our perception is imperfect, as factors beyond bottom-up sensory information influence how we perceive the world. So, what kind of top-down processes influence perception?
How expectations influence perception of pain
One way researchers study perception is through pain. We typically think of pain as a sensation resulting from damage to the body, such as burns or cuts. However, the experience of pain is also constructed; meaning, it can be influenced by many factors, including our expectations.
In one study, researchers used thoughtful experimental design to examine the impact of expectations on the perception of pain. This study involved five groups, all of which were exposed to a painful stimulus in a controlled laboratory setting, but each group differed in important ways.
Group 1 served as a baseline or comparison group. They were exposed to pain, without receiving any verbal instructions or drugs.
Group 2 was told they were given a drug that decreases pain but in reality, they received a placebo (a substance with no pain-alleviating effect).
Group 3 was told they were given a drug that increases pain, but were really given a placebo.
With Groups 2 and 3, the researchers tested the effect of expectations on pain perception – expecting either increased or decreased pain due to a drug, despite no actual drug effects. Interestingly, when comparing the self-reported experience of pain in Groups 2 and 3 with that of Group 1, researchers found the perception of pain changed in accordance with the verbal expectations they were given!
Group 4 was told they were given a drug that decreased pain and actually received a drug with that effect. In this case, the expectation matched the effect of the drug.
Finally, Group 5 was told they were given a drug that increased pain, but were actually administered a drug that decreased pain. Group 5 is important because their expectation (increased pain) contradicted the drug’s actual effect (decreased pain). Take a moment – how do you think this will impact their experience of pain? Will the effect of the drug beat out their expectation of increased pain?
For Group 4, researchers found that the expectation of decreased pain AND the drug that decreased pain, together decreased the perception of pain even more than expectation alone (as seen in Group 2). However, for Group 5, the expectation of increased pain canceled out the effect of the drug that decreased pain! Group 5 really highlights the power of top-down processes, like expectations, in significantly shaping our perception.
Awareness of constructed perception and these top-down processes, like expectations, can be a powerful reminder to be curious and ask “why” when differences in perception arise. For me, these research findings also offer another take home message: the “accuracy” of one’s perception often doesn’t matter; perception results in experienced reality, which can have a profound impact on our experience of pain, emotions, and even mental health.
Why is perception influenced by top-down processes? Is this adaptive?
Indeed, it is. If our brain was simply a stimulus-response organ, it would be extremely slow. For example, our vision operates with a delay of approximately 100 milliseconds. It takes time for light to hit the retina in our eyes, get converted into neuronal signals, be processed by the visual system, and eventually result in vision. If our brain waited until then to initiate a response, we would definitely fail to pass a volleyball.
Instead, our brain initiates a cascade of predictions about what might happen in the immediate future. Importantly, these predictions are based on past experiences, recent sensory information, as well as top-down processes like expectations, emotions, and attention. These predictions allow our brain to anticipate what sensory information we are likely to encounter. The “winning” prediction becomes our perception and reality. When the actual sensory information finally arrives, it hopefully confirms the prediction, but if it doesn’t, the brain updates its prediction.
While most of the time the story generated by our brains through predictions matches the real world, it is important to remember our perception is susceptible to influence. Stay tuned for part 2, where we discuss the role of constructed perception in mental health.
Edited by Joe Vuletich and Brianna Best
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