Which of the following symptoms would likely indicate someone is using hallucinogens?

Experiencing vivid illusions or altered perceptions is a hallmark symptom of hallucinogen use. Hallucinogens, such as LSD, psilocybin mushrooms, and mescaline, are substances that significantly alter an individual's sensory experiences and perceptions of reality. Users often report seeing, hearing, or feeling things that are not present, which is a direct result of the drug's impact on the brain’s processing of information. This altered state can lead to a wide range of experiences, from visual distortions to profound changes in thought patterns.

The other options reflect cognitive abilities and mental states that are generally inconsistent with the effects of hallucinogens. Clear reasoning and composure, focused attention at all times, and improved memory retention do not align with the typical experiences of someone under the influence of hallucinogens, where cognitive functions can be disrupted, and reality may become distorted.