Intriguing new study reveals positive emotions follow a classical psychophysical law

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A study has found evidence that some emotional responses adhere to Weber’s law, a psychophysiological principle that governs human perception of various sensations. In experiments where participants assessed emotional intensity, it was found that as the level of pleasantness increased, the accuracy of their judgments diminished. The study was published in Emotion.

Weber’s Law, also known as the Weber-Fechner law, is a fundamental principle in psychology and psychophysics that describes the relationship between the intensity of a physical stimulus and the perceived magnitude of the sensation it produces. It states that the smallest detectable change in the intensity of a stimulus, is proportional to the initial intensity of the stimulus. As the intensity of a stimulus increases, the amount of change required for a person to notice the difference also increases.

The law was named after Ernst Heinrich Weber, a 19th-century German physiologist and anatomist. Weber initially formulated the law in the context of weightlifting. It was later applied to the measurement of sensations by one of his students – Gustav Theodor Fechner, who went to develop the science of psychophysics starting from this law.

Weber’s law underwent extensive testing throughout the 19th and much of the 20th century, primarily in the realm of sensory perceptions like light, taste, sound, pain, and heat. While emotional perception is also a well-researched area, it remains uncertain whether emotions conform to Weber’s law in the same manner as these sensory perceptions.

In their new study, Rotem Berkovich and Nachshon Meiran set out to test whether Weber’s law refers to emotional feelings as well and to develop an accurate way of measuring the intensity of these feelings that would start from a real 0-point (unlike the most commonly used rating scales that have arbitrary starting points). They relied on a conceptual model called linear ballistic accumulator.

Essentially, this model states that the brain accumulates evidence and it makes a decision when there is enough evidence to make it. The more intense a stimulus is, the more its perception can vary, making it harder to differentiate between very intense stimuli than between stimuli of low intensity.

“I find it fascinating to take a topic that seems so ‘spiritual’ such as our emotions, and yet to be able to quantify it,” said Berkovich, a PhD student.

The study involved 34 undergraduate students, 29 of whom were female, recruited through Ben Gurion University’s online system. The researchers utilized a unique experimental procedure designed to mask its actual purpose and minimize demand characteristics. Participants were informed that the research explored how emotions might influence performance in a pure perceptual task, keeping the true nature of the study concealed.

Two main tasks were administered to the participants: an emotion task and a perceptual task.

In the emotional task, participants viewed images pre-determined to evoke specific emotions of varying intensities. They reported whether each image made them feel pleasant or unpleasant by pressing one of two keys, with researchers recording their responses and response times.

In the perceptual task, participants were shown a circle and their task was to indicate whether the next circle presented to them was larger or smaller than the previous one. Each circle area was 5% larger or 5% smaller than the previous one. Participants participated in these experiments on their own personal computers at home.

The results suggest that applying the linear ballistic accumulation model to predict emotional reports is as valid as using it for perceptual decisions, its original intended application. This implies that both the perception of emotions and sensory stimuli are governed by the same principle: Weber’s law. The study found that as emotions (induced by pictures) became more pleasant, the accuracy with which participants gauged their intensity decreased. This supported the notion that pleasant emotions reach awareness in the same ways ordinary sensations do.

The findings provide evidence that “emotions are a form of perception; we become aware of our emotions just as we become aware of our other senses. Additionally, we become less accurate in estimating the intensity of our pleasant emotional experiences as the experience becomes more pleasant,” Berkovich told PsyPost.

However, this pattern did not hold for unpleasant emotions. “We believed that both pleasant and unpleasant emotional feelings follow Weber’s law, but in this study we found that only pleasant emotional feelings follow this law,” Berkovich said.

This might be because accurately detecting small differences in negative emotions becomes crucial for survival as their intensity increases. For example, correctly distinguishing between two highly fearful situations could be a matter of life or death.

“Using computational modeling, we suggest a novel ratio scale [a scale that starts with a real 0, a complete absence of the measured property] that reflects the rate of emotion-related evidence accumulation. Second, this tool allows us to provide one of the strongest supports for James’ perceptual theory [the James-Lange theory of emotions] by showing that pleasant feelings obey Weber’s law. This finding suggests that the process that underlies emotional awareness resembles the process that underlies usual sensory perception, as James has suggested,” the study authors concluded.

The study makes a valuable contribution to the psychological theory about measurement of emotions. However, it also has limitations that need to be taken into account. Notably, the study was conducted on a very small group of participants, consisting almost exclusively of young females.

Additionally, the range of emotion intensities that can be induced using pictures is limited. On the other hand, the Weber-Fechner law is one of the best-established laws in psychology. It is likely that results would remain essentially the same on larger samples and using a broader range of emotion intensities.

The paper, “Pleasant Emotional Feelings Follow One of the Most Basic Psychophysical Laws (Weber’s Law) as Most Sensations Do”, was authored by Rotem Berkovich and Nachshon Meiran.

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