Change detection in the flicker paradigm: Do faces have an advantage?

Changes to a scene that occur during an eye movement, image flicker, or movie cut are difficult to detect. One way to measure change detection performance is with the flicker paradigm, where changes between two images are introduced during a brief blank screen, which causes the images to “flicker”. Ro, Russell, and Lavie (2001) presented flickering displays consisting of one face and five different common objects. They found that changes to faces were detected both more rapidly and more accurately than changes to objects and suggested that faces capture attention due to their biological significance. In the present studies, we found that changes to objects were more readily detected than changes to faces when displays consisted of an object among a number of faces. That is, a change detection advantage was observed for the “odd-one-out” in the array, regardless of its significance. Therefore, faces may not have a special status for change detection.     

Gaze cues influence the allocation of attention in natural scene viewing

In two experiments we examined whether the allocation of attention in natural scene viewing is influenced by the gaze cues (head and eye direction) of an individual appearing in the scene. Each experiment employed a variant of the flicker paradigm in which alternating versions of a scene and a modified version of that scene were separated by a brief blank field. In Experiment 1, participants were able to detect the change made to the scene sooner when an individual appearing in the scene was gazing at the changing object than when the individual was absent, gazing straight ahead, or gazing at a nonchanging object. In addition, participants' ability to detect change deteriorated linearly as the changing object was located progressively further from the line of regard of the gazer. Experiment 2 replicated this change detection advantage of gaze-cued objects in a modified procedure using more critical scenes, a forced-choice change/no-change decision, and accuracy as the dependent variable. These findings establish that in the perception of static natural scenes and in a change detection task, attention is preferentially allocated to objects that are the target of another's social attention.     

Gaze cues influence the allocation of attention in natural scene viewing

In two experiments we examined whether the allocation of attention in natural scene viewing is influenced by the gaze cues (head and eye direction) of an individual appearing in the scene. Each experiment employed a variant of the flicker paradigm in which alternating versions of a scene and a modified version of that scene were separated by a brief blank field. In Experiment 1, participants were able to detect the change made to the scene sooner when an individual appearing in the scene was gazing at the changing object than when the individual was absent, gazing straight ahead, or gazing at a nonchanging object. In addition, participants' ability to detect change deteriorated linearly as the changing object was located progressively further from the line of regard of the gazer. Experiment 2 replicated this change detection advantage of gaze-cued objects in a modified procedure using more critical scenes, a forced-choice change/no-change decision, and accuracy as the dependent variable. These findings establish that in the perception of static natural scenes and in a change detection task, attention is preferentially allocated to objects that are the target of another's social attention.     

The relationship between online visual representation of a scene and long-term scene memory

In 3 experiments the author investigated the relationship between the online visual representation of natural scenes and long-term visual memory. In a change detection task, a target object either changed or remained the same from an initial image of a natural scene to a test image. Two types of changes were possible: rotation in depth, or replacement by another object from the same basic-level category. Change detection during online scene viewing was compared with change detection after delay of 1 trial (Experiments 2A and 2B) until the end of the study session (Experiment 1) or 24 hr (Experiment 3). There was little or no decline in change detection performance from online viewing to a delay of 1 trial or delay until the end of the session, and change detection remained well above chance after 24 hr. These results demonstrate that long-term memory for visual detail in a scene is robust.     

Change detection in the flicker paradigm: The role of fixation position within the scene

Eye movements were monitored while participants performed a change detection task with images of natural scenes. An initial and a modified scene image were displayed in alternation, separated by a blank interval (flicker paradigm). In the modified image, a single target object was changed either by deleting that object from the scene or by rotating that object 90 degrees in depth. In Experiment 1, fixation position at detection was more likely to be in the target object region than in any other region of the scene. In Experiment 2, participants detected scene changes more accurately, with fewer false alarms, and more quickly when allowed to move their eyes in the scene than when required to maintain central fixation. These data suggest a major role for fixation position in the detection of changes to natural scenes across discrete views.     

Scene structure enhances change detection

Theories of objects recognition, scene perception, and neural representation of scenes imply that jumbling a coherent scene should reduce change detection. However, evidence from the change detection literature questions whether jumbling affects change detection. The experiments reported here demonstrate that jumbling does, in fact, reduce change detection. In Experiments 1 and 2, change detection was better for normal scenes than for jumbled scenes. In Experiment 3, inversion failed to interfere with change detection, demonstrating that the disruption of surface and object continuity inherent to jumbling is responsible for reduced change detection. These findings provide a crucial commonality between change detection research and theories of scene perception and neural representation. We also discuss why previous research may have failed to find effects of jumbling.     

Attending but not seeing: The "other race" effect in face and person perception studied through change blindness

We used a change blindness paradigm to examine the “other race” effect in perception. White Caucasian and Indian Asian participants viewed scenes in which White Caucasian and Indian Asian students were present. Changes were made either to the faces of the students, to their bodies or to an independent object in the background. Changes in faces were detected faster than changes in the bodies, which were in turn detected faster than changes in the background. For face detection there was a crossover interaction, with changes in White Caucasian faces detected faster than changes in Indian Asian faces by White Caucasian participants, whilst the opposite result occurred for changes in Indian Asian faces. In contrast, there was no effect of race on the detection of body-part changes or on the detection of changes to background objects. The results suggest that participants of both races attended equally well to subjects from the other race in the scene, but despite this they remained less sensitive to “other race” faces. Change blindness can provide a useful way of analysing attentional and memorial processes in social contexts.     

The Role of Fixation Position in Detecting Scene Changes Across Saccades

Target objects presented within color images of naturalistic scenes were deleted or rotated during a saccade to or from the target object or to a control region of the scene. Despite instructions to memorize the details of the scenes and to monitor for object changes, viewers frequently failed to notice the changes. However, the failure to detect change was mediated by three other important factors: First, accuracy generally increased as the distance between the changing region and the fixation immediately before or after the change decreased. Second, changes were sometimes initially missed, but subsequently noticed when the changed region was later refixated. Third, when an object disappeared from a scene, detection of that disappearance was greatly improved when the deletion occurred during the saccade toward that object. These results suggest that fixation position and saccade direction play an important role in determining whether changes will be detected. It appears that more information can be retained across views than has been suggested by previous studies.     

Semantic consistency versus perceptual salience in visual scenes: Findings from change detection

In a one-shot change detection task, we investigated the relationship between semantic properties (high consistency, i.e., diagnosticity, versus inconsistency with regard to gist) and perceptual properties (high versus low salience) of objects in guiding attention in visual scenes and in constructing scene representations. To produce the change an object was added or deleted in either the right or left half of coloured drawings of daily-life events. Diagnostic object deletions were more accurately detected than inconsistent ones, indicating rapid inclusion into early scene representation for the most predictable objects. Detection was faster and more accurate for high salience than for low salience changes. An advantage was found for diagnostic object changes in the high salience condition, although it was limited to additions when considering response speed. For inconsistent objects of high salience, deletions were detected faster than additions. These findings may indicate that objects are primarily selected on a perceptual basis with subsequent and supplementary effect of semantic consistency, in the sense of facilitation due to object diagnosticity or lengthening of processing time due to inconsistency.     

Spatial updating according to a fixed reference direction of a briefly viewed layout

Three experiments examined the role of reference directions in spatial updating. Participants briefly viewed an array of five objects. A non-egocentric reference direction was primed by placing a stick under two objects in the array at the time of learning. After a short interval, participants detected which object had been moved at a novel view that was caused by table rotation or by their own locomotion. The stick was removed at test. The results showed that detection of position change was better when an object not on the stick was moved than when an object on the stick was moved. Furthermore change detection was better in the observer locomotion condition than in the table rotation condition only when an object on the stick was moved but not when an object not on the stick was moved. These results indicated that when the reference direction was not accurately indicated in the test scene, detection of position change was impaired but this impairment was less in the observer locomotion condition. These results suggest that people not only represent objects’ locations with respect to a fixed reference direction but also represent and update their orientation according to the same reference direction, which can be used to recover the accurate reference direction and facilitate detection of position change when no accurate reference direction is presented in the test scene.     

Semantic Informativeness Mediates the Detection of Changes in Natural Scenes

Three experiments investigated whether the semantic informativeness of a scene region (object) influences its representation between successive views. In Experiment 1, a scene and a modified version of that scene were presented in alternation, separated by a brief retention interval. A changed object was either semantically consistent with the scene (non-informative) or inconsistent (informative). Change detection latency was shorter in the semantically inconsistent versus consistent condition. In Experiment 2, eye movements were eliminated by presenting a single cycle of the change sequence. Detection accuracy was higher for inconsistent versus consistent objects. This inconsistent object advantage was obtained when the potential strategy of selectively encoding inconsistent objects was no longer advantageous (Experiment 3). These results indicate that the semantic properties of an object influence whether the representation of that object is maintained between views of a scene, and this influence is not caused solely by the differential allocation of eye fixations to the changing region. The potential cognitive mechanisms supporting this effect are discussed.     

The effect of spatial and nonspatial contextual information on visual object memory

Recent research has found visual object memory can be stored as part of a larger scene representation rather than independently of scene context. The present study examined how spatial and nonspatial contextual information modulate visual object memory. Two experiments tested participants’ visual memory by using a change detection task in which a target object's orientation was either the same as it appeared during initial viewing or changed. In addition, we examined the effect of spatial and nonspatial contextual manipulations on change detection performance. The results revealed that visual object representations can be maintained reliably after viewing arrays of objects. Moreover, change detection performance was significantly higher when either spatial or nonspatial contextual information remained the same in the test image. We concluded that while processing complex visual stimuli such as object arrays, visual object memory can be stored as part of a comprehensive scene representation, and both spatial and nonspatial contextual changes modulate visual memory retrieval and comparison.     

The influence of color on the perception of scene gist

In 3 experiments the authors used a new contextual bias paradigm to explore how quickly information is extracted from a scene to activate gist, whether color contributes to this activation, and how color contributes, if it does. Participants were shown a brief presentation of a scene followed by the name of a target object. The target object could be consistent or inconsistent with scene gist but was never actually present in the scene. Scene gist activation was operationalized as the degree to which participants respond "yes" to consistent versus inconsistent objects, reflecting a response bias produced by scene gist. Experiment 1 demonstrated that scene gist is activated after a 42-ms exposure and that the strength of the activation increases with longer presentation durations. Experiments 2 and 3 explored the contribution of color to the activation of scene gist. The results revealed that color has an influence across a wide variety of scenes and is directly associated with scene gist.     

Developmental changes in children's understanding of the similarity between photographs and their referents

In a series of three experiments, we investigated the development of children's understanding of the similarities between photographs and their referents. Based on prior work on the development of analogical understanding (e.g. Gentner & Rattermann, 1991), we suggest that the appreciation of this relation involves multiple levels. Photographs are similar to their referents both in terms of the constituent objects and in terms of the relations among these objects. We predicted that children would appreciate object similarity (whether photographs depict the same objects as in the referent scene) before they would appreciate relational similarity (whether photographs depict the objects in the same spatial positions as in the referent scene). To test this hypothesis, we presented 3-, 4-, 5-, 6-, and 7-year-old children and adults with several candidate photographs of an arrangement of objects. Participants were asked to choose which of the photographs was 'the same' as the arrangement. We manipulated the types of information the photographs preserved about the referent objects. One set of photographs did not preserve the object properties of the scene. Another set of photographs preserved the object properties of the scene, but not the relational similarity, such that the original objects were depicted but occupied different spatial positions in the arrangement. As predicted, younger children based their choices of the photographs largely on object similarity, whereas older children and adults also took relational similarity into account. Results are discussed in terms of the development of children's appreciation of different levels of similarity.     

Detection and Identification of Change in Naturalistic Scenes

Research using change detection paradigms has demonstrated that only limited scene information remains available for conscious report following initial inspection of a scene. Previous researchers have found higher change identification rates for deletions of parts of objects in line drawings of scenes than additions. Other researchers, however, have found an asymmetry in the opposite direction for addition/deletion of whole objects in line drawings of scenes. Experiment 1 investigated subjects' accuracy in detecting and identifying changes made to successive views of high quality photographs of naturalistic scenes that involved the addition and deletion of objects, colour changes to objects, and changes to the spatial location of objects. Identification accuracy for deletions from scenes was highest, with lower identification rates for object additions and colour changes, and the lowest rates for identification of location changes. Data further suggested that change identification rates for the presence/absence of objects were a function of the number of identical items present in the scene. Experiment 2 examined this possibility further, and also investigated whether the higher identification rates for deletions found in Experiment 1 were found for changes involving whole objects or parts of objects. Results showed higher identification rates for deletions, but only where a unique object was deleted from a scene. The presence of an identical object in the scene abolished this deletion identification advantage. Results further showed that the deletion/addition asymmetry occurs both when the objects are parts of a larger object and when they are entire objects in the scene.     

Semantic guidance of attention within natural scenes

When viewing real-world scenes composed of a myriad of objects, detecting changes can be quite difficult, especially when transients are masked. In general, changes are noticed more quickly and accurately if they occur at the currently (or a recently) attended location. Here, we examine the effects of explicit and implicit semantic cues on the guidance of attention in a change detection task. Participants first attempted to read aloud a briefly presented prime word, then looked for a difference between two alternating versions of a real-world scene. Helpful primes named the object that changed, while misdirecting primes named another (unchanging) object in the picture. Robust effects were found for both explicit and implicit priming conditions, with helpful primes yielding faster change detection times than misdirecting or neutral primes. This demonstrates that observers are able to use higher order semantic information as a cue to guide attention within a natural scene, even when the semantic information is presented outside of explicit awareness.     

Emergence of drawing devices for total and partial occlusion: a longitudinal study

The developmental emergence of two drawing devices was investigated in young children: the use of omission (ie not drawing any of a hidden object) to depict total occlusion and the use of hidden line elimination (HLE, ie deleting only that part of an object that is hidden from view) to depict partial occlusion in a three-dimensional scene. Three groups of school children (5, 6, and 7 years old) were tested individually with two tasks four times over a 2-year period. One task called for the omission device (to draw a cup with its handle not in view) and the other for the HLE device (to draw one ball behind and partially occluded by another). The stimuli in each task were presented in pairs, with one member of the pair showing the occluded scene and the other a canonical or not-occluded scene. Changes in the strategies used by the children to indicate the visual differences within the pairs were recorded over the four testing sessions. Children were found to use the omission device more readily with the cup task than the HLE device with the ball task. There was an age-related trend in every task in the use of the drawing device appropriate to that task. For those who did not use the drawing device appropriate for a perspective drawing, there was a tendency for each age group to favour a particular strategy for representation. The advantage of using a longitudinal design to chart the developmental trend of the emergence of these two drawing devices is discussed.     

Failures of retrieval and comparison constrain change detection in natural scenes

In a change detection paradigm, a target object in a natural scene either rotated in depth, was replaced by another object token, or remained the same. Change detection performance was reliably higher when a target postcue allowed participants to restrict retrieval and comparison processes to the target object (Experiment 1). Change detection performance remained excellent when the target object was not attended at change (Experiment 2) and when a concurrent verbal working memory load minimized the possibility of verbal encoding (Experiment 3). Together, these data demonstrate that visual representations accumulate in memory from attended objects as the eyes and attention are oriented within a scene and that change blindness derives, at least in part, from retrieval and comparison failure.     

Eye movements during change detection: implications for search constraints, memory limitations, and scanning strategies

Search, memory, and strategy constraints on change detection were analyzed in terms of oculomotor variables. Observers viewed a repeating sequence of three displays (Scene 1-->Mask-->Scene 2-->Mask...) and indicated the presence-absence of a changing object between Scenes 1 and 2. Scenes depicted real-world objects arranged on a surface. Manipulations included set size (one, three, or nine items) and the orientation of the changing objects (similar or different). Eye movements increased with the number of potentially changing objects in the scene, with this set size effect suggesting a relationship between change detection and search. A preferential fixation analysis determined that memory constraints are better described by the operation comparing the pre- and postchange objects than as a capacity limitation, and a scanpath analysis revealed a change detection strategy relying on the peripheral encoding and comparison of display items. These findings support a signal-in-noise interpretation of change detection in which the signal varies with the similarity of the changing objects and the noise is determined by the distractor objects and scene background.