nbs presentation response feedback

Response Matching

Presentation Version 0.47 introduced features on targets and runtime response classification that function differently from previous versions. What the program does depends on the value of the response_matching header parameter. To maintain backward compatibility, the default value of this parameter corresponds to the behavior defined in previous versions of Presentation. If you want to use the new features, you must define this header parameter as simple_matching. Most of this section assumes that response_matching = simple_matching . At the end of this section, we describe differences between the older and current behaviors.

Presentation can associate responses with stimuli at runtime and can monitor performance. A stimulus must be response active to be associated with a response. There are two types of response active stimuli: targets, and response active non-targets.

To make a stimulus event a target , define the target_button stimulus event parameter. The value of this parameter defines the number(s) of the response button(s) which will be considered as a correct response for that stimulus event . Response button numbers begin with 1, and the number of a response button is determined by its order in the Active Buttons box on the Response panel . You can define multiple correct responses for a target by separating them with commas.

If a stimulus is not a target , but may be associated with a response, you can make it a response active non-target. To do this, define the response_active stimulus event parameter to be true.

stimulus_time_in and stimulus_time_out

Response active stimuli are active for a specified time interval within a trial , and possibly past the end of the trial. Responses are associated with response active stimuli only during their active period. That time interval is specified by the stimulus_time_in and stimulus_time_out stimulus event parameters. These values are times in milliseconds relative to the actual presentation time of the stimulus. You can assign the special value never to stimulus_time_out . If you don't assign these parameters, Presentation uses the values of the default_stimulus_time_in and default_stimulus_time_out header parameters. Once a response is associated with an active stimulus, that stimulus is no longer active.

The clear_active_stimuli trial parameter controls the clearing of any active stimuli when a trial ends. If clear_active_stimuli is true and a trial ends for any reason, all active stimuli are cleared. If false , the stimuli will remain active until the time out time is reached or a subsequent trial with clear_active_stimuli true ends. The default value if you don't define it is the value of the default_clear_active_stimuli header parameter.

WARNING: The value of stimulus_time_in must be less than the value of stimulus_time_out .

Response and Stimulus Classification

You may have multiple stimuli that are response active simultaneously. If a response occurs while multiple stimuli are response active, the response will be associated with the stimulus that became active first. Note that, because of the stimulus_time_in parameter, this is not necessarily the stimulus that actually occurred first.

In the preceding example, pic1 will become active at time = 1300 , while pic2 will become active at time = 1100 . If a response occurs at time = 1500 , it will be associated with pic2 , and pic1 will remain active. See the next section, Feedback , for information about how to make what happens after a response occurs dependent on what the response was.

Both responses and response active stimuli are classified as one of the following types:

stimulus classifications

• hit - the stimulus was a target and was associated with a correct response
• incorrect - the stimulus was a target and was associated with a response that was not correct
• miss - the stimulus was a target and was not associated with a response
• false alarm - the stimulus was an active non-target and was associated with a response
• other - the stimulus was not any of the above

response classifications

• hit - the response was associated with a target for which it was the correct response
• incorrect - the response was associated with a target but it was not the correct response
• false alarm - the response was associated with a response active non-target
• other - the response was none of the above

If a trial ends when a stimulus is waiting to become active, Presentation does not classify that stimulus as a miss . If the response is classified as a hit and the header parameter target_button_codes is defined, the event code and port code for the response are determined by that parameter rather than from the button_codes header parameter.

Access to Response Active Stimulus Information

The classification of responses can affect the length of trials and the selection of feedback trials .

When a response is associated with a response active stimulus, Presentation calculates the reaction time. This is the time of the response minus the time of the associated stimulus. You can access this value as well as classification information at runtime in PCL by using the response_data , stimulus_data , program_response_manager , and program_stimulus_manager PCL types. You can also have response active stimulus information written to the logfile by checking the Stimulus List checkbox in the Logfiles panel . A response active stimulus will appear in this list even if it is not associated with an event code . However, a stimulus will only appear in the logfile general event list if it has an event code .

Ignoring Responses

You may choose to ignore responses that occur when there are no response active stimuli. If the all_responses stimulus event parameter is false , and there are no stimuli that are currently response active, responses will be ignored for the purposes of determining when a trial ends and the automated selection of a feedback trial .

In the preceding example, if a response occurs before pic1 is displayed, the trial will not end.

When all_responses = false , data about all responses that occur may still appear in the logfile . If you do not want these responses reported in the logfile , set the response_logging header parameter to log_active .

legacy_matching

If you don't define the response_matching header parameter, it receives the default value of legacy_matching, indicating the behavior prior to Presentation version 0.47. This mode differs from simple_matching mode in the following respects:

• only targets are response active
• stimulus_time_in and stimulus_time_out are not used
• only correct responses are associated with targets
• responses that occur when no targets are active are classified as false alarms

In the case of legacy_matching, then, stimuli and responses are classified in the following way:

legacy_matching stimulus classifications

Legacy_matching response classifications.

• incorrect - there was an active target, but it was not the correct response
• false alarm - the response was given when no targets were active

For example:

If button 1 is pressed first, the response will be classified as incorrect and the target pic1 will remain active. If button 2 is then pressed, it will be classified as a hit and be associated with the target .