Optimized Mnemonic Similarity Task (omst)
AKA: Continuous Mnemonic Similarity Task
Background
The original Mnemonic Similarity Task (MST) is a sensitive measure for memory changes across the life span and has proven extremely successful for the early detection of memory impairments. It was developed by Shauna M. Stark and colleagues in 2013 and focuses on the impact of event similarity on episodic memory. While the MST shows to be a highly sensitive instrument to assess early memory impairments not detected by traditional recognition memory measures, the administration of the procedure proved difficult for clinical purposes or large-scale testing. For one, the task is rather long and tiring for participants and attention may slip. In addition, the two-phase setup requires participants to keep track of several sets of instructions (and a shift in response requirements), further adding complexity and potentially requiring more hands-on help from testing administrators.
In 2023, Stark et al revised the format of the task to run a single phase procedure to reduce task complexity and cut down testing time. Furthermore, the revised task comes with more stimuli subsets and testing variations that allow easier retesting and tracking memory changes for large scale testing projects such as run by pharmaceutical companies. The revised task has become known as the Optimized Mnemonic Similarity Task (oMST) or - because of its single phase design - as the continuous MST.
The single phase of the oMST presents a sequence of 128 objects. For each object, participants have to decide whether the object is NEW ('never seen before'), OLD ('previously seen') or SIMILAR ('a similar object has been seen but not the exact same one'). The 'trick' of the oMST is that some objects are repeated once (OLD), some are never repeated (NEW), and some items are similar to a previously presented object (SIMILAR). Note that the same object can be classified as NEW (first presentation) and OLD (second presentation).
Stark et al could show that the oMST provides an equivalent level of diagnostic sensitivity to the classic MST while reducing total testing time by more than half.
Task Procedure
After a short practice phase that runs 5 guided and 4 unguided trials to familiarize participants with the basic task of the oMST, the test phase starts. A sequence of 128 images are presented to the participants one-by-one. Each image is presented for 2s and participants have up to 1 minute to decide whether the item was NEW, SIMILAR, or OLD. Of the 128 trials, 64 trials have the correct response NEW, 44 have the correct response SIMILAR and 20 have the correct response OLD (so of the 64 NEW items, 20 are repeated to become OLD, and 44 are 'rerun' by similar images).
What it Measures
The oMST is a tool to measure episodic memory impairments
Psychological domains
- Episodic Memory: Ability to remember a specific personal event in time.
- Recognition Memory: Capability to correctly identify previously encountered stimuli among unfamiliar distractors.
- Visual Long-Term Memory: Durability and storage capacity of high-detail visual representations over time
- Object Recognition: Lower-level visual processing required to categorize what an object is
- Sustained Attention: Ability to maintain focus across a continuous stream of dozens of visual stimuli to catch subtle differences.
Main Performance Metrics
- LDI: Lure Discrimination Index, comparison metric of proportion correctly identified Lures and foils that have been incorrectly categorized as Lures; Main MST measure (also referred to as Lure Discrimination Index
- TRI: Traditional Recognition Index, comparison metric of proportion correctly identified Targets and foils that have been incorrectly categorized as Targets
Psychiatric Conditions
oMST performance has been found to be impaired in the following patient groups
- Mild Cognitive Impairment (MCI)
- Asymptomatic/Preclinical AD Risk Groups
- Alzheimer’s Disease (AD)
- Parkinson’s Disease (PD)
- Major Depressive Disorder (MDD)
- Schizophrenia
Test Variations
The oMST is a continous form of the classic Mnemonic Similarity Task (MST), an object recognition test sensitive to changes in memory performance. Whereas the MST uses a two phase testing paradigm, the oMST combines both phases into a single one (thus it's also referred to as the continuous MST), cutting down on testing time. This script provides the oMST run with stimuli set 1 (3 different trial orders provided)
This script runs the oMST with stimuli set 2 (3 different trial orders provided)
This script runs the oMST with stimuli set 3 (3 different trial orders provided)
This script runs the oMST with stimuli set 4 (3 different trial orders provided)
This script runs the oMST with stimuli set 5 (3 different trial orders provided)
This script runs the oMST with stimuli set 6 (3 different trial orders provided)
References
Search Google Scholar for peer-reviewed, published research using the Inquisit Optimized Mnemonic Similarity Task (omst).
Stark CEL, Noche JA, Ebersberger JR, Mayer L and Stark SM (2023) Optimizing the mnemonic similarity task for efficient, widespread use. Front. Behav. Neurosci. 17:1080366. doi: 10.3389/fnbeh.2023.1080366