Pacificación y paz

Individual Statements

The second hypothesis for this investigation, repeated below, anticipates a change in the subjects’

qualitative perception of their own performance.

H5.2 A change in subjects’ qualitative perception of their own performance and preference across a range ofsegmentationdegrees

By collating the results from the post-presentation subjective questionnaire statements, four box-and-whisker plots were generated, as shown in figure5.8, with the responses converted into a Likert-scale ordering on the vertical axis and thesegmentationdegree shown along the horizontal axis.

Q1: "I was confident that I saw all the targets."

(a)Confidence Q2: "I found the task challenging."

1 Q3: "I found the size of the images..."

(c)Image Size Q4: "I found the rate of the images..."

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1

1 1

(d)Presentation Rate

Interquartile Range Median Value Number of Outliers

Figure 5.8– Responses to the post-presentation subjective statements averaged by segmentation degree for the preliminary experiment

A surprising result from the subjective results in figure5.8is the consistency between subjects.

The blue boxes in figure5.8represent 50% of the responses, with the dots beyond the whiskers of the plot indicating outliers (more than 1.5× the outside the interquartile range above the upper quartile and below the lower quartile) which consist of less than 3% of the results.

The confidence that subjects had in seeing all thetargets(statement in figure5.5a, responses in figure 5.8a) was low. Withsegmentationdegree 1, the response was centred on the middle option of “Neither” with 50% of the subjects indicating a small preference o ne-way (“Agree”) or the other (“Disagree”). With an increase insegmentationdegree, the variation in responses was reduced with the majority of subjects indicating low confidence with segmentationdegree 6, as

demonstrated by 75% of responses being between “Neither” and “Strongly Disagree”.

Subjects found the task of findingtargetsdifficult regardless ofsegmentationdegree, ranging from the majority responding between “Neither” and “Agree” forsegmentationdegree 1 to the extreme ofsegmentationdegree 6 where every subject responded between “Agree” and “Strongly Agree” to finding the task difficult (statement in figure5.5b, responses in figure5.8b).

The remaining two post-presentation subjective questionnaire statements analysed the per-ception of image size (statement in figure5.5c, responses in figure5.8c) and presentation rate (statement in figure5.5d, responses in figure5.8d). As thesegmentationdegree is increased, the image size is reduced and the presentation rate increased. Therefore it is unsurprising that subjects responded indicating these exact trends in size and rate. However, the purpose behind the state-ments was to evaluate the trends in the data, which are of interest. Subjects foundsegmentation degrees 2–6 “Small” in size and “Fast” in presentation rate. Onlysegmentationdegree 1 was found to be “Okay” by the majority of subjects.

The trends acrosssegmentationdegree are clear, as are the links between the statements. As segmentationdegree is increased, subjects’targetconfidence (figure5.8a) decreases. A smaller perceived image size (from “Large”–“Too Small”) as shown in figure5.8c, correlates with the lack of confidence in correctly identifying all thetargets. The other correlation exists between

“task challenge” and presentation rate. As thesegmentationdegree is increased, subjects perceive the presentation increasing (from “Okay”–“Too Fast”), figure5.8d, and also feel that the “task challenge” increased (from “Neither”–“Agree”, figure5.8b).

Trial Comparisons

At the end of each randomised experiment, the subject was shown a review of all six trials they had observed together with two comparison questions (figure 5.6) in which they could only vote for a single trial (i.e.segmentationdegree). Collating these responses indicates that subjects perceived that they were most successful withsegmentationdegree 1 (seven responses, figure5.9a).

Two outliers indicated a preference for the opposite extreme ofsegmentationdegree 6. Subjects were then asked which presentation method they would like to use to maximise theirtarget identification abilities. Thesegmentationdegree with the most votes was perhaps surprisingly

segmentationdegree 2 (five responses, figure5.9b). While subjects felt they were most successful withsegmentationdegree 1, they preferred a slightly faster presentation rate with a slight reduction in image size, i.e.segmentationdegree 2.

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"Out of the six sequences you saw today, at which do you think you were most successful?"

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"Out of the six sequences you saw today, which did you prefer?"

Figure 5.9– Responses to the post-experiment subjective questions, with each subject able to vote for one trial (i.e. segmentation degree) per question

Subjective Results Analysis

The second hypothesis (H5.2) is accepted: subjects do report a change in perception between segmentationdegrees. in comparison to the previous experiment, these results provide clearer an-swers and therefore the methodology is deemed to be sound for the second, primary investigation.

The fact that with the increase insegmentationdegree subjects found the task more challenging and were less confident in theirvisual inspectionrole, suggests that a degree of fatigue may be to blame. Therefore the revised experiment should incorporate a fatigue statement.

The slight preference amongst subjects forsegmentationdegree 2 is indicative that subjects can see the merit in this presentation method for assisting them with their task of searching for human beings within naturalistic stimuli.

5.5.4 Eye-Movement Analysis

The third and final hypothesis associated with this investigation is repeated below.

H5.3 A distinct change in eye-movement behaviour across different degrees ofsegmentation A difference in eye-movements was anticipated from the analysis of the previousSVP experi-ment where the locations offixationswere specifically analysed.

Since all the presentation methods under test were forms of staticRSVPs, the centre of the monitor is the dominant location forfixations, as can be seen from the heat-maps in figure5.10.

These heat-maps show the locations offixationsacross all trials and subjects, grouped by seg-mentationdegree. In addition for the HVSto position the eye towards the centre of a changing stimulus (Tatler2007), there is an increased liklihood of atargetoccurring near the centre of the screen as opposed to the edge of the display. As thesegmentationdegree is increased, thefixations are less spread across the tile, particularly forsegmentationdegrees 3–6 (figures5.10c–5.10f).

This reduction in the spread offixationscan be summarised with figure5.11, where the average eye-movement velocity per trial is plotted againstsegmentationdegree. For comparison, velocities are presented, however because the duration of each trial is identical, the velocities shown in figure 5.11 are scaled versions of the scan-path length per trial. The results which vary from 24.1^○/s forsegmentationdegree 1 to 8.65^○/s forsegmentationdegree 6 indicate a similar fall in eye-movement velocity with decreasing tile-size (and hence increasingsegmentationdegree).

Therefore the third hypothesis is accepted. The eye-movement behaviour associated with segmentationdegree 1 (identical to theSVPmode at 90 mph) appears distinct (an average eye-movement velocity of 24.1^○/s per trial spread across the entire display, figure 5.10a) from the behaviour exhibited withsegmentationdegrees 3–6. With these threesegmentationdegrees, an eye-movement velocity range of 8.21–9.78^○/s per trial was observed, mostly constrained to the 2^○circle shown in each heat-map in figure5.10(indicating the area of the display projected on the observers’ foveal region if they were to stare at the centre of the screen), regardless of the tile dimensions. Segmentation degree 2 appears to be a transitionary point between these two trends, with an average eye-movement velocity of 15.6^○/s per trial observed, covering the majority of the 11.3× 8.51^○tile, shown by the rectangle in figure5.10b.

5.6 Refinements