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Why indecisive trials matter: Improving the binocular rivalry imagery priming score for the assessment of aphantasia

DOI: 10.3758/s13428-025-02780-6
Tags:
Object ImageryObjective MeasuresSpatial Imagery
1 more
Monzel, M., Scholz, C. O., Pearson, J., & Reuter, M. (2025). Why indecisive trials matter: improving the binocular rivalry imagery priming score for the assessment of aphantasia. Behavior Research Methods, 57(9). doi:10.3758/s13428-025-02780-6

Abstract

Since mental imagery cannot be observed from the outside, it is all the more important to make it measurable. Yet, many so-called mental imagery tasks confuse object and spatial imagery or can be solved entirely without mental imagery, making them inappropriate for the assessment of mental imagery strength. One promising measurement method is the binocular rivalry task by Pearson et al. (Current Biology 18(13):982–986, 2008), which uses mental imagery priming to quantify mental imagery strength. Here, we propose an improved equation for the binocular rivalry priming score to significantly increase its predictive validity. In a sample of 38 aphantasics and 73 controls, we demonstrate that the binocular rivalry priming score calculated by the new equation explains more variance in the self-reported mental imagery capacity than the original equation. The improved binocular rivalry priming score is particularly beneficial when only a few trials are recorded (e.g., due to time or attention constraints) or when people with low mental imagery (i.e., aphantasics) have to be identified. The improved binocular rivalry priming score is advantageous in many situations, making it the preferred measure for future research.

Authors

  • Merlin Monzel30
  • Christian O. Scholz5
  • Joel Pearson33
  • Martin Reuter16

What This Study Is About

Researchers wanted to find a more accurate way to measure mental imagery—the ability to picture things in your mind—by fixing a math problem in a popular vision test. They specifically wanted to see if this new method could better identify people with aphantasia, often described as having a "blind mind’s eye."

How They Studied It

The team looked at 111 participants: 38 with aphantasia and 73 "controls" (people who can visualize). They used a classic experiment called a binocular rivalry task.
Imagine wearing 3D glasses where one eye sees red stripes and the other sees blue. Your brain can’t merge them, so it flips back and forth between the two. However, if you imagine the color red *before* the test, your brain is "primed" to see red. In the past, if a participant saw a messy "mixed" blur of both colors, scientists threw that data away. In this study, the researchers created a new formula to include those "indecisive" trials instead of ignoring them.

What They Found

The new math worked! By including the mixed trials, the test became much more reliable. The researchers found:
  • The new formula was significantly better at matching how participants described their own imagery in surveys.
  • People with aphantasia showed almost no "priming" effect. Because they don't form a mental image, their brain doesn't get a "head start" on seeing one color over the other.
  • The test is now much more efficient, meaning scientists can get accurate results using fewer trials.

What This Might Mean

This suggests that binocular rivalry is one of our best "objective" tools for studying aphantasia because it doesn't just rely on what people *say* they see—it measures how their brain actually processes light.
However, we should be careful: while this new math is a better "ruler" for measuring groups, the study suggests it’s still not quite perfect enough to "diagnose" aphantasia in a single person with 100% certainty. It’s a huge step forward, but science is a marathon, not a sprint!

One Interesting Detail

The researchers found that for people with aphantasia, their vision was actually *more* stable. Because they don't have internal mental images "flickering" in the background, their brains weren't as easily distracted, leading to a more consistent view of the world during the test!
This summary was generated by AI and may contain errors. Always refer to the original paper for accuracy.