Object Substitution Research Articles

Asymmetry in object substitution masking occurs relative to the direction of spatial attention shift.

A sparse mask that persists beyond the duration of a target can reduce its visibility, a phenomenon called object substitution masking. Y. Jiang and M. M. Chun (2001a) found an asymmetric pattern of substitution masking such that a mask on the peripheral side of the target caused stronger substitution masking than on the central side. Assuming spatial attention was focused toward the target, the peripheral and central masks were located in the same and opposite direction of an attentional path with reference to the target in their study. We hypothesized that this asymmetric mask configuration relative to the attentional shift contributes to asymmetric substitution masking. To test this hypothesis, we conducted four experiments among which the presence or absence of the center-periphery relationship and the presence or absence of the asymmetric mask configuration were manipulated independently and orthogonally. The results suggest that asymmetric substitution masking occurs relative to the direction of spatial attention irrespective of the central-peripheral relation. We propose that the asymmetry in substitution masking might be explained by attentional momentum associated with orienting toward the target.

How does target duration affect object substitution masking?

Object substitution masking (OSM) is typically studied using a brief search display. The target item may be indicated by a cue/mask surrounding but not overlapping it. Report of the target is reduced when mask offset trails target offset rather than being simultaneous with it. We report 5 experiments investigating whether OSM can be obtained if the search display is on view for a period of up to 830 ms but cueing of the target location is delayed. The question of interest is whether OSM must reflect the initial response of the visual system to target onset or whether it can arise in other ways, possibly during the transition from a pre-attentive representation of the target item to an attentional representation of it. Our results show that OSM decreases in strength as target duration increases. An explanation is suggested in terms of the object individuation hypothesis (Lleras & Moore, 2003).

Objects with reduced visibility still contribute to size averaging

People can rapidly judge the average size of a collection of objects with considerable accuracy. In this study, we tested whether this size-averaging process relies on relatively early object representations or on later object representations that have undergone iterative processing. We asked participants to judge the average size of a set of circles and, in some conditions, presented two additional circles that were either smaller or larger than the average. The additional circles were surrounded by four-dot masks that either lingered longer than the circle array, preventing further processing with object substitution masking (OSM), or disappeared simultaneously with the circle array, allowing the circle representation to reach later visual processing stages. Surprisingly, estimation of average circle size was modulated by both visible circles and circles whose visibility was impaired by OSM. There was also no correlation across participants between the influence of the masked circles and susceptibility to OSM. These findings suggest that relatively early representations of objects can contribute to the size-averaging process despite their reduced visibility.

Endogenous cueing attenuates object substitution masking

Object substitution masking (OSM) is a form of visual masking in which a briefly presented target surrounded by four small dots is masked by the continuing presence of the four dots after target offset. A major parameter in the prediction of OSM is the time required for attention to be directed to the target following its onset. Object substitution theory (Di Lollo et al. in J Exp Psychol Gen 129:481-507, 2000) predicts that the sooner attention can be focused at the target's location, the less masking will ensue. However, recently Luiga and Bachmann (Psychol Res 71:634-640, 2007) presented evidence that precueing of attention to the target location prior to target-plus-mask onset by means of a central (endogenous) arrow cue does not reduce OSM. When attention was cued exogenously, OSM was attenuated. Based on these results, Luiga and Bachmann argued that object substitution theory should be adapted by differentiating the ways of directing attention to the target location. The goal of the present study was to further examine the dissociation between the effects of endogenous and exogenous precueing on OSM. Contrary to Luiga and Bachmann, our results show that prior shifts of attention to the target location initiated by both exogenous and endogenous cues reduce OSM as predicted by object substitution theory and its computational model CMOS.

Recovery of a crowded object by masking the flankers: Determining the locus of feature integration

Object recognition is a central function of the visual system. As a first step, the features of an object are registered; these independently encoded features are then bound together to form a single representation. Here we investigate the locus of this "feature integration" by examining crowding, a striking breakdown of this process. Crowding, an inability to identify a peripheral target surrounded by flankers, results from "excessive integration" of target and flanker features. We presented a standard crowding display with a target C flanked by four flanker C's in the periphery. We then masked only the flankers (but not the target) with one of three kinds of masks-noise, metacontrast, and object substitution-each of which interferes at progressively higher levels of visual processing. With noise and metacontrast masks (low-level masking), the crowded target was recovered, whereas with object substitution masks (high-level masking), it was not. This places a clear upper bound on the locus of interference in crowding suggesting that crowding is not a low-level phenomenon. We conclude that feature integration, which underlies crowding, occurs prior to the locus of object substitution masking. Further, our results indicate that the integrity of the flankers, but not their identification, is crucial for crowding to occur.

Exercise enhances hippocampal‐dependent learning in the rat: Evidence for a BDNF‐related mechanism

Short periods of forced exercise have been reported to selectively induce enhancements in hippocampal-dependent cognitive function, possibly via brain-derived neurotrophic factor (BDNF)-mediated mechanisms. In this study, we report that 1 week of treadmill running significantly enhanced both object displacement (spatial) and object substitution (nonspatial) learning. These behavioral changes were accompanied by increased expression of BDNF protein in the dentate gyrus, hippocampus, and perirhinal cortex. The effects of exercise on object substitution were mimicked by intracerebroventricular injection of BDNF protein. These data are consistent with the hypothesis that exercise has the potential to enhance cognitive function in young healthy rats, possibly via a mechanism involving increased BDNF expression in specific brain regions.

Pretend play, social competence and involvement in children aged 5–7 years: The concurrent validity of the Child‐Initiated Pretend Play Assessment

The aims of this study were to investigate the relationship between pretend play, social competence and involvement in school-based activities in children aged 5-7 years and to determine whether children's social competence and level of involvement could be inferred from their scores on the Child-Initiated Pretend Play Assessment. The pretend play skills of 41 primary school-aged children aged 5-7 years were assessed on a one-on-one basis. Classroom teachers of the children assessed the children's social competence using the Penn Interactive Peer Play Scale and their involvement in school based activities using the Leuven Involvement Scale for Young Children. Significant positive relationships were found between elaborate pretend play and object substitution scores, involvement scores and peer play interaction scores (P < 0.05, P < 0.01). A significant negative relationship was found between elaborate pretend play scores, and social disconnection and social disruption scores (P < 0.05). Play deficit indicators were significantly negatively related to involvement scores (P < 0.01). This suggests that children with proficient pretend play skills are socially competent with peers and are able to engage in classroom activity. Children who scored poorly on the play assessment were more likely to have difficulty interacting with their peers and engaging in school activities. Social competence and involvement skills are related to a child's ability to engage in pretend play. A child's social skills and ability to engage in school activities as assessed by teachers can be inferred from their scores on the Child-Initiated Pretend Play Assessment.

Object substitution masking induced by illusory masks: Evidence for higher object-level locus of interference.

A briefly presented target can be rendered invisible by a lingering sparse mask that does not even touch it. This form of visual backward masking, called object substitution masking, is thought to occur at the object level of processing. However, it remains unclear whether object-level interference alone produces substitution masking because previous studies manipulated only the presence or absence of a physical masking stimulus after the removal of the target, leaving the possibility of some image-level interference contributing to the total masking. To assess object-level interference in the present study, we used an illusory-contour figure as an object mask, adjacent to the possible target locations, which was created by rotating 4 previewed inducers shaped like Pac-Man to face inward to form a subjective square region. The illusory object persisting beyond the target offset reduced the visibility of the target only when presented in its immediate vicinity. This masking effect could not be attributed to the local directional changes, symmetry, or perceptual closure of the inducers near the target. These results provide strong evidence for a high-level locus of interference in object substitution masking.

Comprehension of pretence in children with autism

Impairments of pretend play are a diagnostic characteristic of autism. This has been interpreted in terms of a generative impairment. Specifically, children with autism are unable to generate the ideas for pretend play despite an intact underlying ability to understand pretence. The notion of a performance deficit affecting production only has, in part, been based upon observations that children with autism appear to have no difficulty understanding pretence. However, research investigating comprehension is somewhat limited and has only investigated a specific type of pretend play, namely pretend properties. The research reported here investigated the ability of children with autism to understand object substitution pretence and pretend gestures (i.e. using no substitutes). Children with autism (N = 36) matched for verbal ability (between 3 and 6 years) with typically developing children (N = 55) and children with moderate learning difficulties (N = 37) were questioned about a series of pretend actions, such as writing. The results revealed three main findings. First, children with autism appear to experience no notable difficulties comprehending functional play. Second, children with autism do encounter difficulties comprehending pretend play. A performance deficit is unable to explain these findings and it is suggested that there may be a more critical impairment in understanding how absent objects are represented. Finally, there was a trend for some kinds of object substitutions and gestures to be more impaired than others. One tentative interpretation is that as the degree of similarity between the referent and the substitute diminishes the representational connection becomes more difficult to understand, particularly when there is a need to inhibit salient but irrelevant cues.

Detecting changes in naturalistic scenes: contextual inconsistency does not influence spontaneous attention in high‐functioning people with autism spectrum disorder

Individuals with autism spectrum disorders (ASD) are often reported to be good at detecting minute changes in the environment. This study tested two factors in this phenomenon; detail-focus and reduced top-down influence of scene-schema expectations on spontaneous attention to visual scene elements. Using a change blindness paradigm, adults with ASD and matched typically developing (TD) adults were presented with images of naturalistic scenes (e.g., living room). Scene changes involved three types of object substitution: an object was replaced with (i) an unexpected scene-unrelated object, (ii) a scene-related object of a different basic-level category, (iii) or a different exemplar of the original object category. Top-down effects of scene-schema expectations should render scene-unrelated (i) substitutions easiest to recognize; detail focus should increase detection of exemplar changes. The TD group showed the expected condition effects, detecting scene-unrelated substitutions significantly better than both types of scene-related changes. By contrast, the ASD group showed no condition effect, and was only significantly slower and less accurate than the TD group in detecting scene-unrelated objects. These findings suggest reduced influence of schematic expectations on spontaneous attention in individuals with ASD. Together with other factors, this may contribute to the tendency to notice "irrelevant" changes in the environment.

Visuomotor memory is independent of conscious awareness of target features

A recent study by our group showed that the scaling of reach trajectories to target size is independent of conscious visual awareness of that intrinsic target property (Binsted et al. in Proc Natl Acad Sci USA 104:12669-12672, 2007). The present investigation sought to extend previous work and determine whether unconscious target information represents a temporally durable or evanescent visuomotor characteristic. To accomplish that objective, we employed Di Lollo et al's (J Exp Psychol Gen 129:481-507, 2000) object substitution masking paradigm and asked participants to complete verbal reports and reaching responses to different sized (1.5, 2.5, 3.5, 4.5, 5.5 cm) targets under masked and non-masked target conditions. To determine whether visuomotor networks retain unconscious target information, reaching trials were cued concurrent with target presentation or 1,000 or 2,000 ms after target presentation. For the perceptual trials, participants readily identified the size of non-masked trials but demonstrated only chance success identifying target size during masked trials. Interestingly, however, reaches directed to non-masked and masked targets exhibited comparable and robust scaling with target size; that is, lawful speed-accuracy relations related to movement planning and execution times were observed regardless of whether participants were aware (i.e., non-masked trials) or unaware (i.e., masked trials) of target size. What is more, the length of the visual delay period used here did not differentially influence the scaling of reach trajectories. These results indicate that a conscious visual percept is not necessary to support motor output and that unconscious visual information persists in visuomotor networks to support the kinematic parameterization of action.

Luminance processing in object substitution masking

We probed how processing of luminance increments and decrements interacts with attention dependent substitution masking. Results showed that a target was identified better when surrounded by an opposite polarity mask as compared to the same polarity mask. Opposite polarity mask decreased an effect of distracters, indicating influence on the time of directing attention to a target. The opposite polarity mask decreased masking when delayed for longer than 100 ms. Stimuli with the same polarity but different contrast showed increased masking with high contrast mask. Luminance processing, particularly polarity processing, probably enables faster formation of distinct object representation, interacting with attentional selection processes in object substitution masking.

Illusory displacement due to object substitution near the consciousness threshold

A briefly presented target shape can be made invisible by the subsequent presentation of a mask that replaces the target. While varying the target-mask interval in order to investigate perception near the consciousness threshold, we discovered a novel visual illusion. At some intervals, the target is clearly visible, but its location is misperceived. By manipulating the mask's size and target's position, we demonstrate that the perceived target location is always displaced to the boundary of a virtual surface defined by the mask contours. Thus, mutual exclusion of surfaces appears as a cause of masking.

Object substitution masking: When does mask preview work?

When a target is enclosed by a 4-dot mask that persists after the target disappears, target identification is worse than it is when the mask terminates with the target. This masking effect is attributed to object substitution masking (OSM). Previewing the mask, however, attenuates OSM. This study investigated specific conditions under which mask preview was, or was not, effective in attenuating masking. In Experiment 1, the interstimulus interval (ISI) between previewed mask offset and target presentation was manipulated. The basic preview effect was replicated; neither ISI nor preview duration influenced target identification performance. In Experiment 2, mask configurations were manipulated. When the mask configuration at preview matched that at target presentation, the preview effect was replicated. New evidence of ineffective mask preview was found: When the two configurations did not match, performance declined. Yet, when the ISI between previewed mask offset and target presentation was removed such that the mask underwent apparent motion, preview was effective despite the configuration mismatch. An interpretation based on object representations provides an excellent account of these data.

Object substitution masking induced by illusory masks: evidence for higher object-level locus of interference

A briefly presented target can be rendered invisible by a lingering sparse mask that does not even touch it. This form of visual backward masking, called object substitution masking, is thought to occur at the object level of processing. However, it remains unclear whether object-level interference alone produces substitution masking because previous studies manipulated only the presence or absence of a physical masking stimulus after the removal of the target, leaving the possibility of some image-level interference contributing to the total masking. To assess object-level interference in the present study, we used an illusory-contour figure as an object mask, adjacent to the possible target locations, which was created by rotating 4 previewed inducers shaped like Pac-Man to face inward to form a subjective square region. The illusory object persisting beyond the target offset reduced the visibility of the target only when presented in its immediate vicinity. This masking effect could not be attributed to the local directional changes, symmetry, or perceptual closure of the inducers near the target. These results provide strong evidence for a high-level locus of interference in object substitution masking.

Disruption of early face recognition processes by object substitution masking

Visual stimuli can fail to reach conscious awareness when surrounded by dots sharing a common onset but remaining visible after target removal, a phenomenon known as object substitution masking (OSM). We assessed the locus of substitution by recording the N170 component of the human event-related potential during a face/house classification task. Delayed-offset dots impaired target categorization, confirming the generality of object substitution masking by extending the effect to realistic, complex stimuli. Furthermore, object substitution masking eliminated the N170 amplitude difference between faces and houses, providing the first neural evidence that object substitution masking disrupts structural encoding stages during object recognition.

The decontextualization of form and function in the development of pretence

Through the process of decontextualization, the behaviours and objects used in children's pretence become increasingly detached from their real‐life contexts and uses (Flavell, 1985). However, whilst age‐related changes in children's pretence have been reasonably well documented, the relationship between the decontextualization of form and function has yet to be established and the relationship between pretence using substitute objects and pretence without substitute objects remains unclear. To address these issues, 3–8‐year‐old typically developing children (N =84) were shown a series of pretend actions, like writing, enacted at various levels of decontextualization. Children's understanding of each action was assessed. The results revealed three main findings. First, form and function are both equally important in children's comprehension of object substitution pretence. Second, children find actions enacted using substitute objects that are similar to the referent in terms of both their form and function easier to interpret than those performed using decontextualized props – including body‐part‐as‐object (BPO) and imaginary object (IO) gestures – regardless of age. Finally, BPO and IO gestures are of equal complexity and children 5 years and above correctly interpret these gestures more readily than actions involving substitute objects that share no similarity with the referent. These findings are discussed in relation to dual and triune representation problems (DeLoache, 1995; Tomasello, Striano, &amp; Rochat, 1999).

Testing models of object substitution with backward masking

A briefly presented visual target stimulus can be difficult to identify if shown in the context of a mask stimulus. There are several quantitative models that have been used to explain many different masking effects. Here, we look at modeling what has been called object substitution. We analyze four models and show that three of the models work with a common principle, whereas the fourth behaves quite differently. The three similar models have previously been used to explain many other aspects of visual masking, whereas the fourth model was designed exclusively to deal with object substitution masking effects. We identify an experimental test on the basis of which to choose between the models. The experimental results support the behavior of the fourth model.

Common-onset masking simulated with a distributed-code model

A distributed-coding model incorporating lateral inhibition in a simulated nerve network has been successful in accounting for many properties of backward masking (Bridgeman, 1971, 1978), linking modeling with neurophysiology and psychophysics. Metacontrast is a variety of backward masking that is of particular interest in uncovering properties of visual coding because target and mask do not overlap in time or space, and it is the first stimulus that is reduced in visibility, not the second. The lateral inhibitory model can also simulate common-onset masking, where a target and mask appear simultaneously but the mask disappears after a variable delay, and it can reproduce qualitatively the effects of attention on object substitution by varying the time interval over which sensory codes are analyzed.

Recovery from object substitution masking induced by transient suppression of visual motion processing: A repetitive transcranial magnetic stimulation study.

Object substitution masking is a form of visual backward masking in which a briefly presented target is rendered invisible by a lingering mask that is too sparse to produce lower image-level interference. Recent studies suggested the importance of an updating process in a higher object-level representation, which should rely on the processing of visual motion, in this masking. Repetitive transcranial magnetic stimulation (rTMS) was used to investigate whether functional suppression of motion processing would selectively reduce substitution masking. rTMS-induced transient functional disruption of cortical area V5/MT+, which is important for motion analysis, or V1, which is reciprocally connected with V5/MT+, produced recovery from masking, whereas sham stimulation did not. Furthermore, masking remained undiminished following rTMS over the region 2 cm posterior to V5/MT+, ruling out nonspecific effects of real stimulation and confirming regional specificity of the rTMS effect. The results suggest that object continuity via the normal function of the visual motion processing system might in part contribute to this masking. The relation of these findings to the reentrant processing view of object substitution masking and other visual phenomena is discussed.