What Happens to Our Brain When We Watch Videos at Faster-Than-Normal Speeds?

Many of us have developed the habit of listening to podcasts, audiobooks, and other digital content at increased playback speeds. For younger audiences, this may even be the norm.

A survey conducted among students in California revealed that 89 percent adjusted the playback speed of their online classes. Meanwhile, media outlets have published numerous stories about the growing popularity of accelerated video consumption.

It is easy to understand the appeal of watching content more quickly. It allows us to consume more material in less time or to review the same content multiple times for deeper understanding.

This approach can be particularly useful in educational settings, where it may free up time to consolidate knowledge, complete practice tests, and engage in other learning activities.

Watching videos at higher speeds may also help sustain attention and interest throughout the content, potentially reducing the likelihood of distraction.

However, there are notable downsides as well.

Cognitive Overload

When a person receives spoken information, researchers typically distinguish between three memory phases: encoding, storing, and later retrieval.

During the encoding phase, the brain needs time to process and understand the stream of words. Words must be extracted, and their contextual meanings retrieved from memory in real time.

The average rate of human speech is approximately 150 words per minute, although doubling that speed to 300 or even tripling it to 450 words per minute remains within the range of intelligibility.

The concern, however, lies with the quality and durability of the memories we form.

Incoming information is temporarily stored in a system called working memory. This system allows fragments of information to be transformed, combined, and manipulated into a format suitable for transfer to long-term memory.

Since working memory has a limited capacity, too much information delivered too quickly can exceed its limits. This leads to cognitive overload and the loss of information.

Speed Watching and Information Retention

A recent meta-analysis examined 24 studies on learning from lecture videos. The designs varied, but most involved playing a video lecture at normal speed (1x) for one group and at increased speeds (1.25x, 1.5x, 2x, and 2.5x) for another.

Like in clinical trials for medical treatments, participants were randomly assigned to each group.

After watching the video, all participants took the same test to assess their knowledge of the material.

The tests included tasks such as recalling information and answering multiple-choice questions to evaluate memory retention.

The meta-analysis showed that increasing playback speed had progressively negative effects on test performance. At speeds up to 1.5x, the decline was minimal. But beginning at 2x, the negative impact ranged from moderate to large.

To put this in perspective, if a group of students had an average test score of 75 percent, with a typical variation of 20 percentage points in either direction, increasing the speed to 1.5x would reduce the average score by 2 points. At 2.5x speed, the average loss would be 17 points.

Age Makes a Difference

Interestingly, one of the studies in the meta-analysis also examined older adults, aged 61 to 94, and found that they were more negatively affected by fast-paced content than younger adults aged 18 to 36.

This may reflect a natural decline in memory capacity, even among otherwise healthy individuals, suggesting that older adults should watch content at normal or slower speeds to compensate.

However, it remains unclear whether regular exposure to fast playback speeds can reduce these negative effects over time.

It is possible that younger adults are simply more accustomed to rapid playback and therefore better equipped to manage the increased cognitive load.

Similarly, this raises the question of whether younger individuals can offset the impact on information retention by using fast playback more frequently.

Another unknown is whether consistently watching videos at high speeds has long-term effects on mental functioning and brain activity.

In theory, these effects could be positive, such as an enhanced ability to handle greater cognitive loads, or negative, such as increased mental fatigue due to sustained cognitive pressure. At present, we lack scientific evidence to answer this question.

One final observation is that even if watching content at, say, 1.5x speed does not impair memory performance, some evidence suggests that the experience is less enjoyable.

This could influence motivation and overall learning engagement, potentially making individuals less inclined to continue learning.

On the other hand, fast playback has become mainstream, and once people grow accustomed to it, it may not pose a problem. With time, further research will likely offer clearer insights into these cognitive processes.