Inspection Time Task
Background
The Inspection Time (IT) task is a psychophysical measure of early visual processing speed, specifically the minimum amount of time an individual needs to reliably identify a simple stimulus. The IT task was originally developed by Douglas Vickers and colleagues in 1972 to measure the speed of information intake within a person's visual system, independent of response time. To this end, the IT task uses the method of constant stimuli, testing a range of stimulus presentation durations, to find people's thresholds to correctly identify the location of the long arm of an asymmetric target stimulus that resembles the Greek letter pie 'π' before it is covered up by a masking stimulus. Participant's discrimination performance is plotted against the respective stimulus duration, which results in a cumulative normal ogive curve: performance increases from chance at very brief durations to perfect at long durations in an S-shaped manner.
Ian Deary significantly advanced the Inspection Time (IT) task by expanding its use from a simple perceptual experiment into a robust tool for studying intelligence and cognitive aging. Millisecond's IT task is based on the published procedure by Dreary et al from 2004, who used the IT task in an fMRI study to identify the "functional anatomy" of the task, showing that it activates specific neural networks in the frontal and cingulate cortex.
Due to very short stimuli durations tested by Dreary et al (2004), it is recommended to run the task on monitors that allow very high refresh rates. For example, the shortest duration tested was 6ms which requires a minimum refresh rate of 160Hz (historically, typical monitors operate a 60Hz refresh rate - thus allowing a new stimulus to appear every 16.67ms - but modern mid-to-high-end monitors might support Variable Refresh Rate (VRR) technology).
Task Procedure
Participants are presented with asymmetric target stimuli that resemble the Greek letter pie 'π' for 15 different durations, starting at 6ms and going up to 200ms, before they are covered up by a masking stimulus for 500ms. One arm of the stimulus is longer than the other and participants need to identify the location of the long arm by pressing the 'A' key (left on QWERTY keyboards) for 'LEFT' or the 'L' key for 'RIGHT'. Participants have as much time as they need to respond. A blank screen (500ms) as well as a fixation cross (500ms) precede the next stimulus presentation.
Each of the 15 stimulus durations is presented 20 times and the order is randomly determined. Half the trials present the long arm on the left side. A short practice session of 25 trials (with performance feedback) familiarizes participants with the procedure.
What it Measures
The Inspection Time (IT) task measures early visual processing speed
Psychological domains
- Visual Information Processing: It measures the time required to make a single, correct visual discrimination.
- Intelligence (g): It provides a measurable link between basic perception and higher-order reasoning.
Main Performance Metrics
- Proportion Correct Responses at each stimulus duration: proportion correct responses to plot against stimulus duration to determine threshold
Psychiatric Conditions
The following patient groups tend to show impaired performance on the IT task:
- Dementia and Mild Cognitive Impairment (MCI)
- Schizophrenia
- Traumatic Brain Injury (TBI)
- Cerebral Palsy
- Intellectual Disability
This implements a Visual Inspection Time Task as described in Dreary et al (2004).
References
Search Google Scholar for peer-reviewed, published research using the Inquisit Inspection Time Task.
Vickers, D., Nettelbeck, T., Willson, R.J., 1972. Perceptual indices of performance: the measurement of ‘‘inspection time’’ and ‘‘noise’’ in the visual system. Perception 1, 263– 295.
Deary, I.J., Stough, C., 1996. Intelligence and inspection time: achievements, prospects and problems. Am. Psychol. 51, 599– 608.
Deary, I.J., Enrico Simonotto, E., Meyer, M., Marshall, A., Ian Marshall, I., Goddard, N. & Wardlawf, J.M. (2004). The functional anatomy of inspection time: an event-related fMRI study. NeuroImage, 22, 1466– 1479.