Time perception in the context of "Time travel"

The specious present is defined as the "supposed time between past and future" or "a present that lasts a short stretch of physical time". The term was coined by E. R. Clay in his 1882 book The Alternative: A Study in Psychology, and cited by William James in The Principles of Psychology. It can be classed as a "thick" conception of time perception, to be contrasted with "thin" conceptions that see the present as instantaneous.

A dream is a succession of images, dynamic scenes and situations, ideas, emotions, and sensations that usually occur involuntarily in the mind during certain stages of sleep. Humans spend about two hours dreaming per night, and each dream lasts around 5–20 minutes, although the dreamer may perceive the dream as being much longer.

The content and function of dreams have been topics of scientific, philosophical and religious interest throughout recorded history. Dream interpretation, practiced by the Babylonians in the third millennium BCE and even earlier by the ancient Sumerians, figures prominently in religious texts in several traditions, and has played a lead role in psychotherapy. Dreamwork is similar, but does not seek to conclude with definite meaning. The scientific study of dreams is called oneirology. Most modern dream study focuses on the neurophysiology of dreams and on proposing and testing hypotheses regarding dream function. It is not known where in the brain dreams originate, if there is a single origin for dreams or if multiple regions of the brain are involved, or what the purpose of dreaming is for the body (or brain or mind).

A hallucination is a perception in the absence of an external context stimulus that has the compelling sense of reality. They are distinguishable from several related phenomena, such as dreaming (REM sleep), which does not involve wakefulness; pseudohallucination, which does not mimic real perception, and is accurately perceived as unreal; illusion, which involves distorted or misinterpreted real perception; and mental imagery, which does not mimic real perception, and is under voluntary control. Hallucinations also differ from "delusional perceptions", in which a correctly sensed and interpreted stimulus (i.e., a real perception) is given some additional significance.

Hallucinations can occur in any sensory modality—visual, auditory, olfactory, gustatory, tactile, proprioceptive, equilibrioceptive, nociceptive, thermoceptive and chronoceptive. Hallucinations are referred to as multimodal if multiple sensory modalities occur.

The effect of cannabis on time perception has been studied with inconclusive results. Studies consistently show that most cannabis users self-report the experience of a slowed perception of time. In the laboratory, researchers have confirmed the effect of cannabis on the perception of time in both humans and animals. Studies have sought to explain how cannabis changes the internal clock. Matthew et al. (1998) looked at the cerebellum, positing a relationship between cerebellar blood flow and the distortion of time perception.

Synesthesia (American English) or synaesthesia (British English) is a perceptual phenomenon in which stimulation of one sensory or cognitive pathway leads to involuntary experiences in other sensory or cognitive pathways. Synesthesia can manifest as a bridge between the five traditional senses, though can also include other perceptions, such as nociception, thermoception, chronoception, and interoception. People with synesthesia are referred to as synesthetes.

Awareness of synesthetic perceptions varies from person to person with the perception of synesthesia differing based on an individual's unique life experiences and the specific type of synesthesia that they have. In one common form of synesthesia, known as grapheme–color synesthesia or color–graphemic synesthesia, letters or numbers are perceived as inherently colored. In spatial-sequence, or number form synesthesia, numbers, months of the year, or days of the week elicit precise locations in space (e.g., 1980 may be "farther away" than 1990), or may appear as a three-dimensional map (clockwise or counterclockwise). Synesthetic associations can occur in any combination and any number of senses or cognitive pathways.