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Experimental Psychology : Out of Your Mind

Proponents such as John B. Watson argued that an experimental focus on behaviour would allow psychology to be respected as a natural science. But not everyone was satisfied with disregarding thoughts and feelings.

Not even other behaviourists.

B.F. Skinner argued that mental processes directly influenced observable behaviours. Although they could not be measured, they needed to be considered to develop a full understanding of behaviour.

So really it was just a matter of time before psychologists tried to break the black box wide open.

De doos van Pandora (De Hem, 1910)

And that brings us to the field of cognitive psychology — the scientific study of mental processes; covering memory, attention, language, perception, and so on.

If history was a simple story, I could tell you that cognitive psychology emerged as a reaction to the overly simplistic tenets of behaviourism. Indeed, you can read accounts of this cognitive revolution. Some of you reading this might argue that I did this in my introduction.

But history errs to chaos. The cognitive revolution is a broadly fair description of American research, though it does not truly describe the state of European research.

I am a psychologist not a historian. Cut me some slack.

Unlike the topics we have discussed so far in this series, there are certain cognitive effects that can be replicated in the comfort of your own home. So, for the following section I’m going to ask you to get involved and try out some of the experiments before you read about them.

I promise it will be worth your time.

If you’re on board, you can begin by testing out the Stroop effect.


Most likely you found the second half of that exercise more difficult than the first.

This provides a helpful opportunity to demonstrate how a psychological phenomenon can be investigated in a scientific manner. Firstly, a hypothesis needs to be made — in this case that participants will find the second task harder than the first.

However, this by itself is not enough. What exactly do we mean by harder? And how can we show this was the case?

To do this we need to operationalise our hypotheses — we need to explicitly state what we are measuring in attempting to prove our point.

For example, you could ask each participant how they found the experiment and draw conclusions from their answers. These responses would provide qualitative data which could be analysed to give an indication of how participants felt about each task.

However, qualitative data can be difficult to work with. It is time-intensive to collect, it relies on participants accurately describing their inner state, and it can be difficult to compare across individuals (for example, two people might have vastly different ideas about what “quite difficult” means).

Instead, many psychologists prefer to work with quantitative data — that is, data in the form of a numerical output.

For example, in this version of the Stroop test, you were timed for each task. The experimenter would easily be able to collate all participants' time scores and produce an average result for each experimental condition (i.e. for when word and colour matched, and for when word and colour did not match).

Statistical tests are then used to see if the times generated differ significantly from one another (i.e. that a difference is present and that it is likely to have been caused by a factor of interest rather than random chance).

So, what exactly has happened here? What do psychologists believe is happening in the Stroop test? Commonly, the results are concluded to demonstrate cognitive interference.

When presented with words our automatic response is to read them – cued by millions of repetitions across our lives. However, the Stroop test asks us to override this automatic processing to perform a separate task. As such, we are required to expend more cognitive processing power and slow down – or simply barrel on through and make more mistakes.

For our next experiment, please watch the video below:


This video demonstrates the effect of ‘inattentional blindness’ — a phenomenon in which we fail to notice a striking and unexpected stimulus, due to our focus being diverted elsewhere.

There have been many demonstrations of inattentional blindness. None are more famous than the Invisible Gorilla experiment presented by Daniel Simon and Christopher Chabris (the inspiration for the Transport for London video above).

Half of Simon and Chabris's participants failed to notice a man in a gorilla costume walk amongst the basketball players and beat his chest. Hence, the invisible gorilla.

But is the gorilla invisible or just unseen? A replication by Jennifer Pappass and colleagues used eye-tracking technology to demonstrate that participants looked directly at the unexpected stimulus and still failed to report it.

Invisible indeed.

There is a great deal of debate as to what exactly drives this effect. For our purposes, the most important takeaway is that our ability to process the world around us is more complex than simply parsing the information that is presented to us.

Simon and Chabris were awarded an Ig Nobel Prize for their eye-catching work — an annual award for research that first makes you laugh and then makes you think. A tremendous award and a worthy winner.

With fresh eyes and a better understanding of the experiment, try watching Simon's own version of the experiment. With the knowledge you have now, can you believe that anyone fell for it?


Be honest — did you catch all of those?

The final effect I’d like to demonstrate is change blindness. I am so confident that this will work, I will even tell you what it is before you try it.

Change blindness occurs when observers fail to notice strikingly large changes in a visual stimulus.

That might not sound clear but watch this video and I’m sure you will understand.

Change blindness is a particularly fascinating phenomenon due to its ability to work in the real world outside of lab conditions. For a great example, please watch this demonstration by English mentalist and illusionist, Derren Brown.

It shows us that we probably have more faith in our day-to-day understanding of the world than perhaps is warranted.

And on that note, we can call time on this introduction to cognitive psychology. If any of these effects have caught your attention, there are many more that can be found online. Some of which might even form the basis of future articles.

So, what’s next in Experimental Psychology 101?

To this point we’ve rather ignored the elephant in the room (quite the menagerie going unnoticed). Humans don’t exist in isolation, and the effect we have on one another can be staggering. So next time we will discuss the exciting (and dangerous) field of social psychology.

Why not whet your appetite for social psychology with a look at one of its most famous studies? Click here to learn about Stanley Milgram’s infamous obedience to authority experiments.


If you’d like to read more about cognitive psychology, check out this article on episodic memory.



Pappas, J. M., Fishel, S. R., Moss, J. D., Hicks, J. M., & Leech, T. D. (2005, September). An eye-tracking approach to inattentional blindness. In Proceedings of the Human Factors and Ergonomics Society Annual Meeting, 49(17), 1658-1662. Sage CA: Los Angeles, CA: SAGE Publications.

Scarpina, F., & Tagini, S. (2017). The Stroop color and word test. Frontiers in Psychology, 8, 557.

Simons, D. J., & Chabris, C. F. (1999). Gorillas in our midst: Sustained inattentional blindness for dynamic events. Perception, 28(9), 1059-1074.

Simons, D. J., & Rensink, R. A. (2005). Change blindness: Past, present, and future. Trends in Cognitive Sciences, 9(1), 16-20.


Image references

De Hem, L. De doos van Pandora (1910) [Pastel].

Author Photo

Sam Ridgeway

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