Suspiciousness perception in dynamic scenes: a comparison of CCTV operators and novices

Christina J Howard,David C Hogg,Iain D Gilchrist,Tom Troscianko,Ardhendu Behera

doi:10.3389/fnhum.2013.00441

Abstract

Perception of scenes has typically been investigated by using static or simplified visual displays. How attention is used to perceive and evaluate dynamic, realistic scenes is more poorly understood, in part due to the problem of comparing eye fixations to moving stimuli across observers. When the task and stimulus is common across observers, consistent fixation location can indicate that that region has high goal-based relevance. Here we investigated these issues when an observer has a specific, and naturalistic, task: closed-circuit television (CCTV) monitoring. We concurrently recorded eye movements and ratings of perceived suspiciousness as different observers watched the same set of clips from real CCTV footage. Trained CCTV operators showed greater consistency in fixation location and greater consistency in suspiciousness judgements than untrained observers. Training appears to increase between-operators consistency by learning “knowing what to look for” in these scenes. We used a novel “Dynamic Area of Focus (DAF)” analysis to show that in CCTV monitoring there is a temporal relationship between eye movements and subsequent manual responses, as we have previously found for a sports video watching task. For trained CCTV operators and for untrained observers, manual responses were most highly related to between-observer eye position spread when a temporal lag was introduced between the fixation and response data. Several hundred milliseconds after between-observer eye positions became most similar, observers tended to push the joystick to indicate perceived suspiciousness. Conversely, several hundred milliseconds after between-observer eye positions became dissimilar, observers tended to rate suspiciousness as low. These data provide further support for this DAF method as an important tool for examining goal-directed fixation behavior when the stimulus is a real moving image.

Highlights

Studies of naturalistic task performance have used eye movements as a measure of attentional deployment (e.g., Land, 1999; Findlay and Gilchrist, 2003; Underwood et al, 2003)
Much less is known about the extent to which attention can be guided by very high-level semantic interpretation of scenes. Another aspect of performance we addressed in the experiments presented here is the effect of expertise since our observers were both trained circuit television (CCTV) operators and untrained undergraduate observers
(t(39) = 3.540, p < 0.01) indicating that CCTV operators were more likely to spend longer periods of time consistently looking at the same part of the screen as one another than was the case for the untrained observers. For this complex task, the Dynamic Area of Focus (DAF) analysis reveals a temporal relationship between eye movements and subsequent manual responses

Summary

Introduction

Studies of naturalistic task performance have used eye movements as a measure of attentional deployment (e.g., Land, 1999; Findlay and Gilchrist, 2003; Underwood et al, 2003). We measure eye movements to investigate such attentional deployment in the context of closed-circuit television (CCTV) monitoring. Recent research has examined human performance in some aspects of CCTV monitoring. Troscianko et al (2004) showed that people were able to anticipate antisocial behavior in the near future from CCTV footage. Others have examined the limitations of the use of CCTV footage in identifying unfamiliar individuals, face recognition appears to be surprisingly resistant to viewpoint changes or poor image quality when individuals are familiar to observers (Bruce et al, 2001)

Methods

Results

Conclusion