In general terms, focus refers to the ability to willingly direct and sustain attention towards any stimulus in one’s environment, while tuning out and ignoring other environmental stimuli.^[1] The ability to focus is an important aspect of overall cognitive function and is critical for learning, memory, and executive function.^[2] Most brain owners are intimately familiar with the concept as well — the amount of focus and attention one is able to sustain at any given time can vary as a function of physical, emotional, and/or cognitive states. Many have experienced the stark contrast between ‘good’ days, when the ability to direct sustained and calm focus in any particular direction comes seemingly without effort, vs. the more scattered, more challenged state of focus and attention after several days’ worth of inadequate sleep or high levels of stress.

Numerous methods have been developed to assess human attention. Some of the major ones include the following:^[3]

The digit span test (DGS), which is primarily a test of working memory, is one of the earliest tests used to measure focus & attention. During a DGS test, participants are asked to repeat a series of random digits, either in the same order that they were revealed, or backwards.

Simple and choice reaction time (simple/choice RT) tests assess cognitive processing speed, which is well-correlated with attention and alertness. RT tests consist of two parts. For the first part (simple RT), participants are timed responding to a predictable stimulus. The second part of the test (choice RT) requires participants to respond in a correct way to one of several different, unanticipated stimuli.^[4]

The Stroop color and word test measures the Stroop effect, which is the delay in reaction time between congruent and incongruent stimuli, such as color-words printed in like vs. different colors.^[5] For example, the word blue, printed in red ink, is an incongruent stimulus that takes longer to cognitively process compared to the word blue, printed in blue ink (congruent stimulus). The delay in reaction time is partially a function of attention and focus.

The emotional Stroop test (E-Stroop) is a variant of the color and word test that instead presents to participants either neutral words, or words that are related to particular emotional states or disorders. The latter, emotion-associated words tend to be named more slowly by participants, with the delay reflecting attention ability.^[6][7]

Research has consistently suggested that physical activity may have an overall positive effect on focus and attention as well as other aspects on cognitive function.^[8] Moreover, the benefits of physical activity on focus and attention do not appear to be limited to any particular age group, since studies have found positive results in participants ranging from elementary school aged children^[9] to adolescents^[10][11] and older adults.^[12]

However, it is worth noting that the strength of the association between exercise and cognitive function reported in studies on healthy populations has recently come under scrutiny, with one umbrella review of randomized controlled trials suggesting that much of the research performed in this field may be less conclusive than advertised.^[13] More research is needed to establish a direct causal relationship between exercise and cognition, at least in healthy populations.

Numerous supplements have been studied for their effects on focus and attention. For most supplements, rigorous trials testing efficacy in large numbers of participants is lacking. Caffeine^[14] and the amino acid L-theanine^[15] are notable exceptions, with a large body of high-quality evidence demonstrating their efficacy for enhancing focus and attention, particularly when taken together.^[16]

The following additional supplements have been studied for their effects on focus & attention:^[17]

• L-Tyrosine: this amino acid has been shown to have positive effects on attention^[18] and cognitive function under stressful conditions.^[19]
• Omega-3 fatty acids: although omega-3 fats such as docosahexaenoic acid (DHA) are essential for, and present at high levels in, the brain, studies on the effects of omega 3 supplements on attention have reported mixed results.^[20][21]
• B vitamins^[22]
• Nitrates^[23]
• Flavonoids and flavones^[17]
• Ginkgo biloba^[24]
• Ginseng^[25]
• Prebiotics^[26]

Healthier diet patterns tend to be associated with improved focus & attention relative to western-style diets rich in saturated fat and refined sugar. High intakes of fish and plant-based foods were associated with increased measures of attention among elderly people in one cross-sectional study.^[27] Observational studies of children and young adults with ADHD have also found links between focus & attention ability and healthier diet patterns. Moreover, overall less-healthy diet patterns have been associated with decreased focus & attention in these age groups.

The effect of an unhealthy diet on focus and attention may also be acute, as suggested by one study that found consumption of a 5- or 7-day high-fat diet was sufficient to impair focus & attention in both healthy^[28] and sedentary^[29] adults. However, most of the evidence on the effect of diet on focus & attention tends to be observational in nature, and overall results have been mixed. More research is needed to determine whether there is a causal relationship between diet and focus & attention in different populations.

The following factors may adversely affect focus & attention:

• Sleep: both acute^[30] and chronic^[31] sleep deprivation can have negative effects on cognition, including focus & attention^[32]
• Chronic stress^[33]
• Infectious disease^[34]
• Depression^[35]
• Addiction and substance abuse^[36][37]
• Incomplete or unresolved tasks^{[38][39][40][41]}
• Rumination^[42]
• Lack of planning^[39]