空间线索

Our ability to select certain information in an environment to process, while ignoring other stimuli, is referred to as attention.

Visual attention can either be overt—where the eyes are consciously aimed towards an object, like a rising full moon—or covert, in which a person notices something that they are not looking at directly.

For example, an individual might be staring at a sign pointing towards the left side of a fork in the road. However, they will still discern a nearby owl further down that path, because that’s the direction they are cued to go. This concept is referred to as spatial cueing—where covert attention is shifted by a particular signal.

Based on previous work by psychologist Michael Posner, this video demonstrates how to execute a computerized spatial cueing task, including how to interpret data investigating a measure of covert visual attention—reaction times across congruent and incongruent trials.

In this experiment, participants must detect and report brief visual targets that showcase focus and subsequent shifts in attention.

During every trial, participants are asked to observe three frames that occur in order: In frame 1, a red fixation cross, made of ½-in. long lines, is located in the center of the display. Two green boxes, each 1 by 1 in., are centered vertically, 1.5 in. away from the edges of the display.

After 100 ms, the second frame appears for this same duration, but this time, the fixation cross is replaced with a cue—a red arrow that points towards one of the two green boxes.

In the third frame, the cue arrow is simultaneously replaced with the fixation cross. In half of the trials, the letter ‘T’ is added to one of the two boxes, whereas the other half contains the letter ‘L’; both are equally distributed. Participants are asked to identify the letter shown.

Following every response, a brief 500-ms inter-trial-interval occurs, and the sequence is repeated for a total of 400 trials.

Here, the trick is that they are either congruent, where the letter appears in the box that the arrow is pointing to 80% of the time, or incongruent, where it appears opposite of the arrow’s direction for 20% of the trials.

The dependent variable is then the time it takes a participant to make a correct response across trial types, which is achieved by simply choosing the letter shown in the box, regardless of the side.

Participants are expected, on average, to be faster at responding during congruent trials compared to incongruent ones, thus showing the advantages associated with cueing the spatial location of where one should focus their attention.

In preparation for the experiment, open the software program and verify that the spatial cueing paradigm is working correctly.

After recruiting participants, bring each one into the lab and explain that the task is designed to investigate the nature of visual attention. Before proceeding, ask them to complete an informed consent form.

To begin, seat the participant in front of the testing computer, with the back of their chair 60 cm away from the monitor. Explain the task instructions and answer any questions.

When the participant is ready, allow them to start the program by pressing the spacebar. Observe them over a few trials to ensure that they are either pressing the key ‘L’ or ‘T’ as soon as the letter appears on the screen.

Leave the testing room as they complete the 400 trials. Halfway through the experiment, provide a 2-min break, making the total task time less than 10 min.

To begin data analysis, first retrieve the captured data that were initially programmed into an output file.

Note that data for the following items should automatically be populated into the table: the trial number, the letter position, the letter type, the condition, the actual response given by the participant, and importantly, the reaction time—measured from the onset of the letter to the keypress.

Next, check whether the responses provided are accurate by adding a column called ‘Accuracy’ to the table. To populate this column, create a formula to compare ‘Letter Type’ with the ‘Response Given’, such that a 1 represents a correct response and 0 indicates an incorrect answer.

Now, verify that the total averaged accuracy values for each participant are above 0.8 to ensure that participants understood the task instructions.

To visualize the data, graph the average reaction times across participants by trial type. Note that they responded about 200 ms faster in congruent compared to incongruent trials.

This difference suggests that the arrow cued participants to attend to a particular spatial location, allowing them to more quickly process and identify the letter when it appeared there.

Now that you are familiar with designing an experiment to examine spatial cueing, let’s examine how researchers have used variations of the paradigm to investigate how attentional ability changes in cases of brain injury along with alterations in task demands.

Studies using functional magnetic resonance imaging indicated that regions within the parietal lobe are involved in the ability to orient attention to a spatial location.

In patients with focal damage due to strokes or tumors, Posner and colleagues discovered that reaction times were longer during incongruent compared to congruent trials and notably, when compared to neurological controls—those with lesions outside of the parietal area—which confirm the functional significance of this region.

Also, as you’ve learned already, the inclusion of cues in the task leads to anticipatory thoughts of where to focus attention, even though those expectations might not be met.

Researchers have adapted the paradigm to identify the kinds of stimuli, like unexpected bright flashes, that may automatically cause attention to shift. Such modifications could benefit individuals that may have trouble focusing under constrained demands, like those with Attention-Deficit-Hyperactivity Disorder.

You’ve just watched JoVE’s introduction to spatial cueing. Now you should have a good understanding of how to design and conduct a covert visual attention paradigm as well as how to analyze and interpret attentional demands when cues are both expected and mismatched.

Thanks for watching!