How does it measure?

Attentiveness

This index measures the number of correct responses (pressing the space bar in response to a target stimulus) during a stimulus presentation or the void period that follows. The Attentiveness Index allows the assessment of correct responses independently of the response time, therefore providing a pure measure of sustained attention. The difference between the target stimuli number and the number of correct responses gives the number of omission errors.

Timeliness

The Timeliness index calculates the number of correct responses given only when the target was present on the screen. According to the National Institute of Mental Health (2012), ADHD problems with attention may be expressed in “difficulties in processing information as quickly and accurately as others”. Traditional measurements in CPTs usually include Response Time (RT) and RT variability. However, these solutions present the stimulus for a very short and fixed period of time; with the response occurring after the stimulus has disappeared. The limitations of such models mean that accurate, but slow participants can be mistakenly diagnosed as inattentive. Often, the same group of participants would respond correctly if allowed more time, whereas patients who truly have attention issues would not respond at all because they are not alert to the target.

Therefore, the measurement of RT per-se, addresses only the ability to respond quickly, but not the ability to respond accurately. The MOXO d-CPT introduces a void period after each stimulus with differing lengths of time for each presented element. As a result, the MOXO d- CPT can distinguish between accurate responses performed with “good timing” (during the target presentation) and “bad timing” responses (made after the target has disappeared). Recognizing these two timing aspects separately corresponds to the two different problems of ADHD described by the National Institute of Mental Health 2012): Responding quickly and responding accurately.

Impulsiveness

This index represents the number of impulsive commissions performed while a non-target stimulus appeared on screen. Typically, commission errors are coded in case of an inappropriate response to the target (e.g., pressing a random key). In contrast, the MOXO d-CPT’s Impulsiveness index considers only pressing on the space bar in response to non-target stimulus as impulsive behavior. All other non-inhibited responses are categorized as hyper-reactive commission.

Hyper-Reactivity

The Hyper-Reactivity index is the total number of all types of commission responses that were not coded as impulsive responses. Such responses include:

  1. Multiple pressing of the space bar in response to either target or non-target stimuli,  commonly interpreted as a measure of motor hyper-responsivity
  2. Random key pressing of any keyboard button other than the space bar

The separation of impulsive commissions from hyper-reactive commissions allows for the identification of multiple sources of response inhibition problems.

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