The Science Behind First Impressions

Most people understand that first impressions matter. Fewer appreciate quite how fast they form, how much they influence everything that follows and how difficult they are to reverse once set.

The science on this is unambiguous and worth understanding in detail, particularly for professionals whose careers depend on how they are perceived by clients, colleagues and leaders.

The Brain Decides in Milliseconds

Research by Princeton psychologists Janine Willis and Alexander Todorov established that people form judgements about a stranger's trustworthiness, competence, likeability, attractiveness, and aggressiveness after viewing their face for just 100 milliseconds, one tenth of a second. Crucially, extending that exposure time did not significantly alter the impressions formed. Longer exposure increased confidence in the judgement, but rarely changed it.

Of all the traits assessed, trustworthiness showed the highest correlation between snap judgements and those formed after extended observation. In other words, the brain's initial read on whether someone can be trusted is both rapid and remarkably stable.

The brain regions involved in this process activate within milliseconds of seeing a new face. Neuroimaging studies have found that the amygdala and prefrontal cortex, responsible for emotional processing and decision-making, respectively, show different patterns of activation depending on whether a face is perceived as trustworthy, competent, or threatening. This happens before conscious evaluation has begun.

Why the Brain Works This Way

These rapid judgements have deep evolutionary roots. The ability to quickly assess whether an unknown person represented a threat or an ally was a critical survival skill for our ancestors. The brain has not discarded this mechanism simply because the modern context has changed.

What has changed is the stakes. In professional environments, the same rapid appraisal system that once helped humans avoid physical danger now shapes hiring decisions, leadership perception, client trust, and negotiation outcomes, often before a single substantive word has been exchanged.

Research shows that in job interviews, observers watching just the first 20 seconds of footage, before candidates had even spoken, were able to accurately predict hiring outcomes based on micro-expressions, posture, and appearance. The interview itself frequently confirmed rather than created the impression already formed.

Why First Impressions Are So Hard to Change

Once a first impression is formed, two powerful psychological forces work to preserve it.

The first is the primacy effect, established through decades of research beginning with psychologist Solomon Asch in 1946. Asch demonstrated that the order in which information is presented dramatically affects overall judgement. Participants who heard identical personality traits listed with positive qualities first formed substantially more favourable impressions than those who heard the same traits in reverse order. The information received first creates an anchor against which everything subsequent is measured.

The second is confirmation bias. Once an impression is formed, people naturally notice and remember information that supports their initial judgement while discounting information that contradicts it. This is not a deliberate process. It happens automatically, below the level of conscious awareness, which is precisely what makes it so persistent.

Together, these forces mean that reversing a poor first impression is not simply a matter of performing better in subsequent interactions. It requires overcoming an existing cognitive framework that is actively working to preserve its original conclusion.

The Halo Effect in Professional Settings

Related to the primacy effect is the halo effect, first documented by psychologist Edward Thorndike in 1920. When one characteristic creates a strong positive initial impression, that impression spreads to unrelated traits. A person perceived as competent in one area is likely to be perceived as competent across other areas, even without evidence. The reverse is equally true.

In professional settings, this means that the quality of an initial encounter, whether a first meeting, a presentation, or even a LinkedIn profile, can colour how everything that follows is interpreted. A strong opening creates a halo that works in someone's favour across future interactions. A weak one creates a shadow that requires substantial evidence to overcome.

What the Research Suggests

The science does not suggest that first impressions are immutable or that people are simply prisoners of initial perception. Research confirms that impressions can be revised, particularly when new information is strongly disconfirming and when the person receiving it is motivated to form an accurate rather than a confirming view.

What the research does make clear is that the cognitive effort required to revise a first impression is significantly greater than the effort required to form one. This asymmetry places a premium on the quality of initial interactions in ways that professional culture frequently underestimates.

Understanding the mechanics of how first impressions form, what sustains them, and what can shift them is not a soft skill. It is a practical literacy that shapes professional outcomes in ways that are measurable, predictable, and grounded in decades of well-replicated research.

Sources

[1] Willis, J. & Todorov, A. (2006). First Impressions: Making Up Your Mind After a 100ms Exposure to a Face. Psychological Science, 17(7), 592-598. Overview: https://www.psychologicalscience.org/observer/how-many-seconds-to-a-first-impression

[2] Frontiers Magazine, Washington University (2018). Neuroscience of First Impressions. https://frontiersmag.wustl.edu/2018/12/21/neuroscience-of-first-impressions/

[3] Wikipedia. First Impression (Psychology). https://en.wikipedia.org/wiki/First_impression_(psychology)

[4] Varsity (2024). Mastering First Impressions: How Your Brain Sizes Up Strangers in 7 Seconds. https://www.varsity.co.uk/science/27468

[5] Asch, S. (1946). Forming impressions of personality. Journal of Abnormal Social Psychology, 41, 258-290. Overview: https://psychology.town/social/first-impressions-art-impression-formation/

[6] Psychology Town (2025). The Art of Impression Formation: First Impressions and Beyond. https://psychology.town/social/first-impressions-art-impression-formation/

[7] Thorndike, E.L. (1920). A constant error in psychological ratings. Journal of Applied Psychology, 4(1), 25-29. Overview: https://www.britannica.com/science/halo-effect