RESULTADOS APLICACIÓN PROPUESTA 2 GREEN IT

Participants were given a plain language statement outlining the purpose of the experiment and asked to sign a consent form. They were then provided with standardised verbal instructions and tested individually in a single session lasting 15-20 minutes. Participants were seated in front of a computer screen at a distance of 57cm with their head placed in an adjustable chin rest to ensure their line of vision was at the centre of the computer screen.

Before each display, a white circle appeared for 300ms at the centre of the display, acting as a fixation point. This was followed by the presentation of a smaller circle for 200ms to assist participants focus attention to the visual display. Stimulus display onset occurred 200ms after fixation point offset (see Figure 1). The duration of the stimulus onset asynchrony (between distractor offset and target onset) was also randomly determined at between 93 and 200ms to reduce the potential for predicting target onset and therefore motor preparation when responding. Nine values (93,100, 139, 145, 153, 180, 185, 193, and 200) were randomly assigned to each trial within a block. Stimuli remained on screen for 3000ms or until participants made their choice response.

A B 300ms 300ms 200ms 200ms 93-200ms 93-200ms

Figure 1. Sample experimental sequences for Experiment 1A (not to scale): A Target alone condition B Target presented with additional item and incongruent distractor item. Two cues were presented to assist participants focus at the centre of the screen prior to the onset of the target alone (A) or the target with additional item and distractor (B)

The experiment consisted of three conditions: target alone, low perceptual load (feature demand condition), and high perceptual load (conjunction demand condition). In the target alone condition, following the fixation point offset a blank screen appeared and remained for a randomly varied interval (93-200ms) followed by the presentation of the target alone (see Figure 1). In the low and high perceptual load conditions, following

interval (93-200ms) followed by the simultaneous presentation of the target and distractor letters (see Figure 1). The participants were advised that the experiment used a go/no-go procedure that required them to make their choice response to the target letter based on the presence of an additional item that was presented simultaneously with the target. Each perceptual load condition consisted of four instructional manipulations which are described below.

In the feature demand condition, in 25% of the trials, participants were required to respond to the target letter when the additional shape was green and to withhold their response when it was red, regardless of whether the item was a circle or a square. In 25% of the trials, participants were asked to respond to the target letter when the additional item was red and to withhold their response when it was green, regardless of whether the shape was a circle or a square. In 25% of the trials participants were asked to respond to the target letter when the additional item was a circle and to withhold their response when it was a square, no matter whether the colour was red or green. In 25% of the trials, participants were asked to respond to the target letter when the additional item was a square and to withhold their response when it was a circle, irrespective of whether the colour was green or red.

In the conjunction demand condition, in 25% of the trials, participants were required to respond to the target letter when it was flanked by a green square and to withhold their response when a green circle, red square, or red circle was presented. In 25% of the trials, participants were required to respond to the target letter when a green circle was

presented with it and to withhold their response when a green square, red square, or red circle was presented. In 25% of trials, participants were required to respond to the target letter when it appeared with a red square and to withhold their response when a red circle, green circle, or green square was presented. In 25% of trials, participants were required to respond to the target letter only when a red circle was presented alongside it and to withhold their response when a red square, green circle, or green square was presented. Therefore, participants were asked to attend to the colour or shape (in the feature demand condition) or to the relevant combination of colour and shape (in the conjunction demand condition) and to respond to the target letter only when the appropriate feature or conjunction of features appeared. Participants were also advised that a distractor letter would appear either above or below the central target display during certain blocks of trials and they were emphatically instructed to ignore it.

Participants were presented with instructions on the computer screen prior to the beginning of each trial block. The instructions advised which feature or conjunction of features needed to appear with the target in order for a response to be made. Participants were instructed to respond as quickly as possible by pressing the left or right button on the gaming control pad; the left index finger for target x and right index finger for target o, and vice versa depending on task requirements. Participants were advised of the importance of both fast reaction times and accuracy when responding. Following the presentation of instructions, participants were required to press the space bar on the keyboard to begin the trial.

There were three block types: target alone, low perceptual load, and high perceptual load. The order of the trials according to distractor/target spatial positions was randomised within each block. Blocks were administered twice, once in forward and once in reverse order. The three conditions were presented in 18 separate blocks and were counterbalanced across all participants. The initial forward order of the blocks was counterbalanced across participants. For example, participant 1: LPL, HPL, TA, then TA, HPL, LPL, participant 2: HPL, LPL, TA, TA, LPL, HPL. Hand-to-response key mapping order was counterbalanced across participants. For the first eight blocks of trials, half of the participants used their left hand to respond to target letter x and their right hand to respond to target letter o, while for the other participants hand-to-target mapping was reversed. For the remaining eight blocks of trials, participants were asked to swap hands corresponding to the opposite target type. Participants were given practice trials prior to the experimental trials. Participants who began with the low perceptual load (feature demand) condition were given a block of 12 practice trials, while those who began with the high perceptual load (conjunction demand) condition were given a block of 24 practice trials followed by the experiment. The decision to use different amounts of practice trials between the feature and conjunction conditions was based on Lavie’s (1995) methodology. Lavie’s participants completed double the number of practice trials in the high perceptual load condition compared to the low perceptual load condition. This was adopted in the current study to ensure results could be as comparable as possible to Lavie’s results. In total, Experiment 1A consisted of 576 experimental trials (18 blocks of 32 trials) and 72 practice trials (two blocks of 12

trials and two blocks of 24 trials). The duration of experiment 1A was around 20 minutes.