Persons using the SCIT are briefly shown a pair of lines on a computer screen and asked to indicate which side is the shortest by pressing a keyboard button. This process is repeated many times while we record their speed of response and the number of errors made. Most people can complete the SCIT within 3-4 minutes.
The 'H' version of the SCIT is used to test high-functioning adults, while the easier 'U' version is used for children and people with known cognitive impairment.
The SCIT is sensitive to small changes in the speed of signal processing and in the effectiveness of signal processing, within subcortical and cortical pathways of the brain. The SCIT is able to detect changes before they begin to noticeably affect an individual’s performance on everyday tasks.
Impaired performance on the SCIT indicates that some of the neural networks were not functioning properly at the time the test was conducted. It does not indicate the reason for the impaired performance. In other words, it is a screening test, not a diagnostic test.
The SCIT has its origins in the ‘Inspection Time Task’ that has been used by psychologists since the 1970’s. The test has been refined in a number of significant ways to make SCIT much quicker and more sensitive than the inspection time task.
The SCIT is one of the rare cognitive tests not influenced by practice, so it can be used to repeatedly test someone over a short period of time. This property makes the SCIT useful for detecting the short-term effects of drugs or medications on cognition.
The SCIT performance of most cognitively normal individuals remains stable over time, so that similar results are obtained when a person is retested months or even years later. This property makes the SCIT useful for detecting decrements or improvements in cognition, such as happens in neurodegenerative diseases or after therapeutic interventions.
Factors that DO NOT influence performance on the SCIT
Sex Provided that they are cognitively normal at the time of testing, all genders perform equally well on the SCIT.
Experience Unlike most other cognitive tests, performance on the SCIT is not influenced by practice (the test-retest reliability is approximately 0.95), so the SCIT can be used to test a participant repeatedly over a short period of time.
Emotional state Performance on the SCIT is not influenced by mild or moderate mood states (anxiety, stress or depression). However, like all cognitive tests, performance on the SCIT is affected by severe mood states.
Level of education Provided that age and IQ are accounted for, a participant's educational status does not affect their performance on the SCIT.
Factors that CAN influence performance on the SCIT
Visual impairment People with cataracts or other forms of visual impairment perform poorly on the SCIT. Participants with myopia or other correctable visual disorders can perform normally if they wear their contact lenses or spectacles.
Age Performance on the SCIT gradually declines with age, but this change can be controlled for by using population norms or by comparing to data obtained from prior tests by the same participant.
Language skills Participants who lack a working knowledge of English can have difficulty understanding the written instructions for the SCIT, and should not be tested unless a translator is available. A Chinese version of the SCIT is available.
Intoxication Performance on the SCIT can be impaired in individuals with a blood alcohol level of 0.05 or higher. It is likely that other recreational, prescribed or elicit drugs will affect performance on the SCIT.
Sleepiness It is preferable to test individuals on the SCIT when they feel rested and alert. Individuals with jetlag or acute sleep deprivation show impaired performance on the SCIT. General tiredness does not affect performance.
Cognitive impairment Individuals with mild-moderate cognitive impairment (with an MMSE score of 24 or less) find the SCIT difficult and are often unable to complete the test.
Movement disorders Individuals with severe osteoarthritis or Parkinsonian symptoms can find it difficult to press the keyboard buttons, which slows their recorded response times.
Systemic inflammation Individuals with untreated Coeliac disease or Crohn's disease perform worse than healthy peers on the SCIT. It is possible that other disorders involving systemic inflammation are also associated with impaired performance.