Discover how a simple neurological test became a window into our fundamental drives and motivations
Imagine standing before a horizontal line drawn on a page, pencil poised to mark its exact center. This seemingly trivial task, once reserved for neurologists' clinics, is now helping scientists measure something profound: your motivation to approach rewards, confront challenges, and engage with the world.
Line bisection, a task developed to detect spatial attention deficits in brain injury patients, has emerged as an unexpected window into approach motivation—the impulse that moves us toward goals, rewards, and challenges 1 . Recent research has transformed our understanding of this simple task, revealing its surprising connection to the asymmetric brain activity that underlies our fundamental motivational tendencies.
This discovery isn't just academic; it offers an efficient, non-invasive way to measure brain states that predict everything from financial risk-taking to emotional resilience.
Left and right hemispheres specialize in different motivational states
Subtle deviations in line bisection reveal hidden motivational drives
Simple test with profound implications for psychology and neurology
The line bisection task has humble beginnings. Neurologists have used it for decades to detect unilateral spatial neglect (USN), a condition where brain-damaged patients fail to acknowledge one side of their visual space 2 .
Interestingly, healthy people don't bisect lines perfectly either. Most right-handed individuals display a slight but consistent leftward bias, a phenomenon dubbed pseudoneglect 3 .
| Population | Bisection Bias | Interpretation |
|---|---|---|
| Healthy right-handed individuals | Leftward ("pseudoneglect") | Normal right hemisphere dominance for spatial attention |
| Left neglect patients | Strong rightward deviation | Underestimation of left space due to right hemisphere damage |
| High approach motivation | Rightward shift from baseline | Increased left prefrontal activity associated with approach |
The link between line bisection and motivation emerged from a fascinating neurological insight: the two cerebral hemispheres specialize in different motivational states.
The left prefrontal cortex becomes more active when we experience approach motivation—the desire to move toward rewarding stimuli, opportunities, or challenges 1 .
The right prefrontal cortex shows greater activity during withdrawal motivation—the impulse to avoid threats or unpleasant situations.
This asymmetric brain activation manifests in subtle spatial biases. Since the right hemisphere directs attention to the left side of space, and the left hemisphere to the right side, heightened left prefrontal activity (from approach motivation) increases attention to the right side of space. This shifts the perceived center of a line rightward 6 .
In 2010, researchers published a groundbreaking study specifically designed to validate line bisection as a neural marker of approach motivation 1 6 .
Examined whether individual differences in baseline prefrontal EEG alpha asymmetry would predict individual differences in line bisection bias. Participants underwent resting EEG measurements followed by a line bisection task.
Investigated whether situational factors known to increase approach-related prefrontal asymmetry would correspondingly increase rightward line bisection bias. The researchers used a challenge manipulation known to trigger approach motivation.
The findings provided compelling evidence for line bisection as a valid marker of approach motivation:
| Experimental Manipulation | Key Finding |
|---|---|
| Baseline EEG asymmetry measurement | Positive correlation between left prefrontal activity and rightward bisection bias |
| Challenge condition for high self-esteem individuals | Significant increase in rightward bisection bias |
| Comparison with EEG measures | Consistent patterns between the measures |
The connection between line bisection and approach motivation reflects sophisticated brain networks. Neuroimaging studies reveal that line bisection activates a right-lateralized fronto-parietal network—the same system damaged in neglect patients 3 .
| Brain Region | Role in Line Bisection | Connection to Motivation |
|---|---|---|
| Dorsolateral Prefrontal Cortex | Modulation of spatial attention networks | Core region for approach motivation; associated with goal-directed behavior |
| Intra-parietal Sulcus | Spatial computation and bisection judgment | Integrates motivational state with spatial perception |
| Frontal Eye Fields | Planning exploration of space | Orients attention toward motivationally relevant stimuli |
| Temporo-Parietal Junction | Reorienting attention to salient events | Detects motivationally significant environmental cues |
When we approach the world with motivation, the dorsolateral prefrontal cortex modulates this network, enhancing attention to the right side of space and producing the characteristic rightward bisection bias 6 .
Researchers have developed virtual reality line bisection tasks that examine how spatial attention operates in simulated environments .
Studies using galvanic vestibular stimulation have demonstrated that artificially manipulating sensory input can shift bisection biases 5 .
Line bisection research requires specific materials and tasks, each serving distinct purposes in measuring spatial attention and motivation:
Materials: 11×8.5-inch paper with 18 horizontal lines, pencil 2
Function: Standard clinical assessment; measures unilateral spatial neglect and pseudoneglect
Materials: VR headset, motion tracking, virtual environment
Function: Assesses spatial attention in immersive simulated environments
Materials: 32-channel EEG setup, electrodes following 10-20 system 6
Function: Measures prefrontal alpha asymmetry as neural correlate of approach motivation
Materials: Electrodes for transcutaneous electrical stimulation 5
Function: Manipulates spatial bias by stimulating vestibular nerves
The transformation of line bisection from a simple neurological test to a tool for measuring motivation exemplifies how basic cognitive neuroscience can yield unexpected insights into human nature.
This research reveals that our spatial perception is deeply entangled with our motivational states—we literally see the world differently when we're motivated to engage with it.
Clinicians might use line bisection to track motivational changes in depression treatment, where approach motivation is often impaired.
Educators could develop simple spatial tasks to identify students' motivational states and adapt teaching strategies accordingly.
Marketers might assess consumer engagement with products through subtle spatial attention measures.
Perhaps most importantly, this research reminds us that our experience of the world—even something as basic as judging the center of a line—is never a perfect reflection of reality. It is shaped by the invisible forces of our brain's organization and our momentary motivational states.
As research continues to unravel the connections between motivation, emotion, and spatial attention, the humble line bisection task stands as a powerful reminder that sometimes the simplest tools can illuminate the most complex aspects of human nature.