Borderline Personality Traits and Interpersonal Synchronization in a Finger-Tapping Study

What appeared to be an almost childishly simple task concealed a much more complex question.

With each tap, researchers were examining how people with more pronounced borderline personality traits coordinate physically and emotionally with another “person” – here, a virtual partner.

Borderline traits and the rhythm of daily social life

Borderline personality traits are not confined to psychiatric textbooks. To varying extents, they occur throughout the general population. They can involve rapidly shifting moods, powerful emotional responses, and difficulty settling after feeling wounded or rejected.

Those with higher levels of these traits may experience relationships as a rollercoaster. At one point, a friend or partner can seem perfect and secure; soon afterwards, they may appear distant, dangerous or without value. Abandonment fears may be intense, while small signs of separation can be experienced as rejection.

A fragile sense of identity may also be present. Some individuals report feeling empty, uncertain or unstable, and unsure of who they truly are. This internal upheaval is sometimes associated with impulsive behaviour, including spending, sex, substance use or other forms of risk-taking.

Researchers have long suspected that such emotional swings might disrupt the subtle coordination that holds social interactions together.

When people automatically walk alongside one another, alter their voice during a conversation, or settle into a common tempo while completing a task, they demonstrate what scientists call “interpersonal synchronization”. It is more than an interesting feature of the nervous system: it helps underpin cooperation, empathy and a fundamental sense of connection.

The finger-tapping experiment

To investigate whether borderline traits were associated with this less visible form of synchrony, Italian researchers created an experiment centred on a straightforward motor exercise: tapping a computer keyboard in time with a sequence of tones.

The research included 206 adults from the general population, whose average age was 24. Approximately two-thirds were women. No participants were recruited through clinical services, and they had not necessarily received a diagnosis of borderline personality disorder. Instead, they filled in a standardised measure, the Personality Assessment Inventory – Borderline Scale, which assesses the extent to which a person displays characteristics linked to borderline personality.

A virtual partner with changing timing

Participants were asked to press the space bar in rhythm with tones produced by a virtual partner. They were unaware that the partner’s behaviour varied between conditions.

• During some trials, the virtual partner made no adjustment whatsoever.
• In other trials, it made slight changes to bring its timing nearer to that of the participant.
• Under the most extreme condition, it became “overly adaptive,” substantially altering its own rhythm in response to the participant’s taps.

At five different levels of adaptivity, the programme sought to minimise the difference between every tap and tone. Researchers then measured the timing discrepancy – known as asynchrony – as an objective indicator of coordination.

Following each condition, participants provided two ratings: the extent to which they felt “in sync” with the virtual partner, and their emotional state. To assess mood, the researchers used a short standard measure, the International Positive and Negative Affect Schedule Short Form.

What the study found

Analysis of the data revealed a clear pattern. Participants with higher borderline personality trait scores synchronised less effectively with the virtual partner. Their taps were generally further from the tones, including when the programme attempted to adjust towards their timing.

Higher borderline traits were linked to greater asynchrony, lower perceived synchrony, and more negative emotions during the task.

This pattern had three dimensions:

Aspect measured	Pattern in those with higher borderline traits
Objective timing	Greater mismatch between taps and tones
Subjective sense of being “in sync”	Reported feeling less coordinated with the partner
Emotional experience	More negative affect during the interaction

The results point to a double difficulty. Physical coordination is poorer in a measurable sense, while the interaction also feels more unpleasant internally. Although the task is neutral and carries little consequence, people with higher borderline traits find the experience of “doing something together” with another agent more difficult and more coloured by negative emotion.

What this suggests about social interactions

The researchers propose that the findings may represent broader challenges in social cognition – the mental abilities that enable people to anticipate others’ behaviour, adapt to it and sustain a shared rhythm.

Emotional dysregulation and unstable relationships may disrupt the fine-grained timing that smooth interactions depend on.

Synchronising with somebody else requires us to manage two ongoing tasks. We must follow our own actions while observing the other person’s behaviour, then adjust flexibly. Higher borderline traits could disrupt several stages of this process: predicting the other person’s movements, believing that they will remain predictable, or staying emotionally steady enough to adapt calmly when timing changes.

In everyday settings, interpersonal synchronization is seldom as orderly as a finger-tapping exercise. Conversations accelerate and slow down; people pause, interrupt or pull back. For a person already anticipating rejection, minor disruptions in timing may seem to prove that they do not fit with others, reinforcing a cycle of tension and withdrawal.

Study limitations and unanswered questions

The experiment used a virtual partner instead of a human one. This approach allowed close control of timing, but it also raises an important question: would the same participants have similar coordination difficulties with a real person sitting next to them?

The volunteers were drawn from a nonclinical sample as well. Many may have had only mild borderline traits, rather than the severity found among people formally diagnosed with borderline personality disorder. Effects within clinical groups may therefore be stronger, different or more complex.

Nevertheless, the study contributes to an expanding body of evidence suggesting that social difficulties associated with borderline traits may arise at very basic levels of timing and coordination, rather than solely through thoughts and language.

Useful terms for understanding the findings

Several central ideas may help make the results clearer:

• Borderline personality traits: Characteristics including fluctuating emotions, abandonment fears and an unstable self-image, which may range from mild to severe.
• Interpersonal synchronization: The process through which people coordinate movements, speech patterns and physiological rhythms while interacting.
• Asynchrony: A difference in timing. In this research, it referred to the delay between a participant’s tap and the virtual partner’s tone.
• Emotional dysregulation: Difficulty controlling intense emotional states and recovering from them.

How this could appear in ordinary life

Imagine a crowd trying to clap together at a concert, or two colleagues completing a joint task side by side. Most people slowly establish a shared pace. For someone with stronger borderline traits, however, this modest adjustment may feel less intuitive. They might speed up, slow down or feel out of time, then understand that discomfort as social rejection or failure.

The same mechanisms can operate in conversation. Slow replies, speaking over someone, or incorrectly interpreting pauses may all move people out of sync. When someone already fears abandonment, these small mismatches could prompt powerful reactions, including sudden anger, shame or an impulse to withdraw before being hurt.

Considering interpersonal synchronization also suggests possible forms of support. Therapy involving structured shared activities, rhythm-based exercises or deliberately paced interactions may help some people develop a more stable sense of timing with others. Low-pressure practices, such as mindful breathing with another person, walking at the same pace or playing turn-taking games, may offer ways to practise coordination.

No individual experiment can account for the full complexity of borderline personality traits. Even so, this finger-tapping study highlights something subtle but significant: for some people, the feeling of being “in time” with another living being may be more vulnerable than it appears.