Critical Thinking

The Experinece Wall Part 2

In my last blog post “The Experience Wall” I spoke about the dangers of clinical experience and I broke up clinical experience into 3 parts.

1)       The perception of clinical events (seeing, hearing, feeling etc)

2)       The memories of those events

3)       The interpretation of those perceptions (cause and effect,etc)

My next three posts will look at each of these three categories in more depth.


It appears that our perceptions of the world are accurate and objective. This however is an illusion. In fact, our brains are wired to see things that we expect to see and miss objects and events which are unexpected.  Christopher Chabris and Daniel Simons provided us with a powerful example of this in their famous “invisible gorilla study“. If you have not tried this experiment yourself click on the link and give it a try before reading further (spoiler alert). In their study subjects watched a video of people passing a basketball and were asked to count the number of passes.goriila In the middle of the game, A person in a gorilla suite walks out, pauses to beat his/her chest, then walks away. About 50% of the people watching the video missed seeing the very obvious gorilla (did you see it?). This phenomenon is called inattentional blindness and we are all susceptible to it. In fact, a recent experiment performed on radiologist demonstrated how they can miss unexpected objects on a film. The researchers inserted a picture of a gorilla into the CT images of a lung. 83% of the radiologist did not see the gorilla (even though it was obvious and they looked right at it). Another common example of missing obvious things occurs when watching movies. Just about every movie has continuity errors (despite the presence of a script supervisor) and most of us never notice it. Several website are dedicated to pointing out these errors.

We miss unexpected objects and events because our brains have a finite ability to focus. For example, if I am focusing on a phone conversation, I have a reduced ability to focus on driving. I have been driving long enough that my unconscious brain can handle most of the routine tasks of driving. However, if something unexpected happens (someone pulls out in front of me) I am less likely to perceive the pending collision. This is why hands free devices do not reduce the risk of driving while talking on a cell phone. The problem is not that our hands are tied up with the phone, it is that our minds are tied up with the conversation.

In contrast if we expect to see certain objects, events or patterns we are likely to perceive them, even if they are not present. This is why sGrilled chessusome will see Jesus in a cheese sandwich (we are programmed to see faces) and hear devil worshiping when listening to stairway to heaven backwards (we are programmed to hear words). It may also be why manual therapists think they can identify small differences in movement and position even though the research suggests that we can not. Michael Shermer talks about this “pattern seeking” tendency in his book and in this Tedtalk.

The take home message is that our perceptions are biased. No matter how hard clinicians attempt to avoid it, we will under perceive unexpected objects and events, and over perceive the expected. All we can do is take this bias into account when we are determining how confident we can be in the accuracy of our experience.


Categories: Critical Thinking

10 replies »

  1. This posting, along with the previous one, “The Experience Wall”, is certainly thought provoking. It brings up many questions about what we value as clinicians or as researchers.

    Why is it that scientific knowledge seems to be more highly valued than procedural knowledge by health practitioners, especially when both are equally necessary for us to be successful in our chosen health careers? (Scientific knowledge can be defined as “theoretical” knowledge or factual information – the type that emerges from studies and research. Procedural knowledge can be defined as “practical” knowledge. ie. how to, when to, and IF to do something. This type of knowledge cannot be taught in school and can be learned only through clinical experience.)

    I agree that in order to be a truly effective practitioner, we must integrate evidence into our clinical practice. However, what does “evidence based practice” really even mean?

    Sackett et al (2000) defines evidence-based practice as “the integration of best research evidence, CLINICAL EXPERTISE and patient values” (emphasis added). They also note that “External clinical evidence can inform, but can never replace individual clinical expertise, and it is this expertise that decides whether the external evidence applies to the patient at all, and if so, how it should be integrated into a clinical decision”

    If you accept the above definition of EBP, then you must accept that “evidence” is not just that which is published in journals and text books. Evidence is as much about clinical experience (which you seem to consider “dangerous”) as it is about patient values, AND research. So although research evidence is certainly important, it is not everything and we cannot deem experiential evidence as invalid or inferior. To do so is to commit a major fallacy.

    In your above post you wrote:

    “The take home message is that our perceptions are biased. No matter how hard clinicians attempt to avoid it, we will under perceive unexpected objects and events, and over perceive the expected. All we can do is take this bias into account when we are determining how confident we can be in the accuracy of our experience.”

    The irony of that statement is this: clinicians are not the only ones who are biased. Researchers are biased, scientists are biased…everyone is biased, including you (and me). How confident of the accuracy of their study can researchers really be when their results are interpreted (and can only be interpreted) through their personal lens and personal or vocational biases?

    That brings up a deeper philosophical question: Is it possible that our senses can be wrong? (The examples you gave in your above post seems to suggest so.) if it is possible that our senses can mislead us, how do we know that anything is in fact what we think it is? And that question applies not just to clinicians but to research scientists as well. We know what we know through our senses only. There is no other way to perceive and interact with the world around besides our senses. (Is there?) Yet if our senses fail us, then what do we really know?

    Another question: Is it possible that research findings could be just as “dangerous” as clinical experience? You broke up clinical experience into 1) perception of clinical events, 2) memories of those events and 3) the interpretation of those perceptions. I must ask this: do researchers not also understand research results through 1) perception 2) memories, and ultimately 3) interpretation of those findings? My point is this – research findings have the potential to be just as valid or invalid as clinical experience has the potential to be valid or invalid. You must acknowledge that and not place research above clinical expertise. Science, just like clinical experience, is NOT infallible. If research and clinical experience are therefore on an equal footing, why are we as physiotherapists and health professionals encouraged to value the science more???

    While it is perhaps foolish to base every clinical decision on “my clinical experience” alone, I would suggest that it’s equally foolish to base every clinical decision on “the literature” or “the research” alone.

    Besides academic dishonesty (which anyone in Academia knows takes place a heck of a lot) research methodology is certainly not devoid of its own problems. My biggest problem with research is that is creates a fictitious world and then attempts to apply the results to the real world. Grouping and sub-grouping, inclusion and exclusion criteria (while important for the control of the study) also serve to include and exclude the whole person. It does not take into consideration every aspect of an individual – and it’s individuals that we see in our daily practice. These individuals are whole people – they don’t leave their emotional states, beliefs, past experiences, fatigue, or stressors the door when they come for therapy. And we know that sometimes (often times) it’s these factors which have a greater impact on treatment outcome than anything else that we do. This is where, in my opinion, clinical experience trumps science. Until science can consider the whole person, (body – mind – emotions – spirit) it will be very difficult to ensure that every single technique and skill that we practice as therapists is supported 100% by science. Science (CPRs, protocols, conclusions from systemic reviews, etc) is simply not sufficient to encompass the complexities of the individuals we work with on a daily basis. Because you and I both know this to be true, I will go so far as to suggest that at this time it is impossible to be a physiotherapist whose entire practice is truly evidence based (according to your limited definition of EBP which seems to equate “evidence” with the literature and research).

    In your previous post, you wrote, “It is easy to criticize the literature while blindly trusting our own experiences.” I believe the opposite is all too true; it is easy to criticize and dismiss clinical expertise while blindly trusting in research science. That being said, science, although certainly not perfect, does have valuable an does have a great deal to offer us physiotherapist. It’s time to drop the illusion of “either-or” and embrace the paradigm of “both-and”. Sackett certainly does.

  2. Thanks for the comment ibk. You are very correct that the scientific process is not perfect. However, it is the best method we have for reducing bias. We use the null hypothesis, randomization, controls, blinding and replication and still bias can creep into literature. With clinical experience we have none of those controls so the bias will be magnified even greater.

    Every student who graduates from a PT school in the US is required to take courses on how to be critical consumers of evidence. They are not required to take courses in how to be critical consumers of their own experience. We need to apply the same standards of critique to both the literature and our experience.

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