The effect of betel nut chewing on contour and object masking

The betel nut is a common stimulant in many Asian countries. We employed the masking task developed by Enns and Di Lollo (Trends in Cognitive Sciences, 4, 345-352, 1997) to investigate the effects of betel nuts on sensory and attentional processing. In the masking task, participants needed to identify a target that was masked by either a contour mask or an object mask. Sensory processing was assessed by examining target identification in the contour mask condition when the target was presented only centrally, whereas attentional processing was assessed by examining target identification in the object mask condition when the target was presented randomly in either a central or a parafoveal location. The results showed that chewing betel nut and chewing gum produced significant contour masking with a large effect size, similar to the pure control condition, in which participants chewed nothing, and the placebo control condition, in which what participants chewed was disguised. This suggests that neither betel nut nor gum affects sensory processing. Alternatively, betel nut chewing could produce a reduction in object masking for the habitual chewers and the nonchewers, suggesting an effect of betel nut on attentional processing. This concentrated attention was also observed in the placebo control condition; thus, it cannot be exclusively driven by the expectation effect. Also, chewing per se reduced the attentional distribution foveally.     

Warning: Attending to a mask may be hazardous to your perception

Object substitution is a type of backward masking that occurs when a mask appears during visual search for a target. We tested the hypothesis that object substitution is an overwriting process triggered by attentional selection of the mask. Impeding attentional selection of a mask by embedding it in an array of distractors eliminated object substitution. Similarly, object substitution did not occur when the mask appeared in advance of the target and, therefore, could not capture attention during search for the target. However, masking was reinstated when the mask was revealed from background contours at the moment of target onset and could therefore capture attention during search. These observations demonstrate that attentional selection of the mask is a necessary step in this type of masking and suggest that object substitution is active overwriting of unattended information triggered by selection of other visual information at a nearby location.     

Competition for consciousness among visual events: the psychophysics of reentrant visual processes

Advances in neuroscience implicate reentrant signaling as the predominant form of communication between brain areas. This principle was used in a series of masking experiments that defy explanation by feed-forward theories. The masking occurs when a brief display of target plus mask is continued with the mask alone. Two masking processes were found: an early process affected by physical factors such as adapting luminance and a later process affected by attentional factors such as set size. This later process is called masking by object substitution, because it occurs whenever there is a mismatch between the reentrant visual representation and the ongoing lower level activity. Iterative reentrant processing was formalized in a computational model that provides an excellent fit to the data. The model provides a more comprehensive account of all forms of visual masking than do the long-held feed-forward views based on inhibitory contour interactions.     

Object substitution masking and the object updating hypothesis

The object updating hypothesis of object substitution masking proposes that the phenomenon arises when the visual system fails to individuate target and mask at the level of object token representations. This hypothesis is tested in two experiments using modifications of the dot mask paradigm developed by Lleras and Moore (2003). Target—mask individuation is manipulated by the presentation of additional display items that influence the linking apparent motion seen between a target and a spatially separated mask (Experiment 1), and by the use of placeholders that maintain the target object’s presence during mask presentation (Experiment 2). Results in both cases are consistent with the updating hypothesis in showing significantly reduced masking when the conditions promoted target—mask individuation. However, in both experiments, some masking was still present under conditions of individuation, an effect we attribute to attentional capture by the mask.     

Visual masking and the recovery phenomenon

Two experiments were carried out to investigate visual masking and target recovery. In the first experiment it was found that with superimposed disks of various sizes masking increases with increasing target-mask similarity and contour proximity. The results of the second study show that the extent of masking produced by a disk, which is slightly larger than the target, is drastically reduced when the mask in turn is followed by a ring, the inner contour of which is contiguous with the contour of the mask. This “facilitation effect” decreases as the interval between the mask and the third stimulus is increased. Target recovery in this situation appears to be brought about as a result of the reduction or elimination of the contour of the mask, which, as the first study has shown, is critical in bringing about the masking effect. The results are discussed in terms of some of the known physiological properties of the visual system.     

Masked-target recovery requires focused attention on the target object

Flashing a homogeneous light mask after the presentation of a masked target reduces the deleterious effects of the mask, a phenomenon often called target recovery. Target recovery has been studied using masking paradigms in which a target object is presented in isolation prior to the presentation of a mask, thus capturing attention. In the present study, we examined whether target recovery is possible when a target does not benefit from attentional capture. We hypothesized that target recovery would be eliminated when a target must compete with distractors for perceptual attention. Replicating classic studies, we observed target recovery when pattern and light masks followed an isolated target. However, target recovery was not observed when a light mask followed a masked visual search target. Furthermore, using an attentional-capture paradigm we found that sudden onset search targets were recoverable whereas nononset targets were not. The present findings indicate that attentional capture by a target prior to masking plays a critical role in the subsequent recovery of the target.     

Non-transient luminance changes do not capture attention

The processing of luminance change is a ubiquitous feature of the human visual system and provides the basis for the rapid orienting of attention to potentially important events (e.g., motion onset, object onset). However, despite its importance for attentional capture, it is not known whether a luminance change attracts attention solely because of its status as a sensory transient or can attract attention at a relatively high cognitive level. In a series of six experiments, we presented visual displays in which a single object underwent a luminance change that was either visible or obscured by a mask. A target then appeared either at the change location or elsewhere. The results showed that the luminance change attracted attention only in the visible condition. This was even observed with the largest change we could generate (> 75 cd/m(2)). These data suggest that the importance of a luminance change is only in its status as a low-level sensory transient.     

Different effects of the two types of spatial pre-cueing: what precisely is “attention” in Di Lollo’s and Enns’ substitution masking theory?

Enns and Di Lollo [Psychological Science, 8 (2), 135-139, 1997] have introduced the object substitution theory of visual masking. Object substitution masking occurs when focusing attention on the target is delayed. However, Posner (Quarterly Journal of Experimental Psychology, 32, 3-25, 1980) has already shown that attention can be directed to a target at least in two ways: intentionally (endogenously) and automatically (exogenously). We conducted two experiments to explore the effects of endogenous and exogenous cues on substitution masking. The results showed that when attention was shifted to the target location automatically (using a local peripheral pre-cue), masking was attenuated. A decrease in target identification dependent on a delay of mask offset, typical to substitution masking, was not observed. However, strong substitution masking occurred when the target location was not pre-cued or when attention was directed to the target location intentionally (using a symbolic pre-cue displayed centrally). The hypothesis of two different mechanisms of attentional control in substitution masking was confirmed.     

Visual masking plays two roles in the attentional blink

When two targets are displayed in rapid visual sequence and masked by trailing patterns, identification accuracy is nearly perfect for the first target but follows a U-shaped pattern over temporal lag for the second target. Three experiments examined the role of visual masking in this attentional blink. Experiment 1 compared integration and interruption masks for both targets. Although either mask was effective in producing the blink when applied to the first target, only the interruption mask was effective when applied to the second target. Experiment 2 showed that integration masking of the second target was ineffective over a wide range of accuracy levels. Combining the two forms of masking in Experiment 3 confirmed the dissociation: A combined mask and only a main effect on accuracy for the first target, whereas it produced a qualitatively different pattern over temporal lag for the second target. These results suggest that representations of the target are substituted in consciousness by that of the interruption mask when visual attention is preoccupied.     

Subjective discriminability of invisibility: A framework for distinguishing perceptual and attentional failures of awareness

Conscious visual perception can fail in many circumstances. However, little is known about the causes and processes leading to failures of visual awareness. In this study, we introduce a new signal detection measure termed subjective discriminability of invisibility (SDI) that allows one to distinguish between subjective blindness due to reduction of sensory signals or to lack of attentional access to sensory signals. The SDI is computed based upon subjective confidence in reporting the absence of a target (i.e., miss and correct rejection trials). Using this new measure, we found that target misses were subjectively indistinguishable from physical absence when contrast reduction, backward masking and flash suppression were used, whereas confidence was appropriately modulated when dual task, attentional blink and spatial uncertainty methods were employed. These results show that failure of visual perception can be identified as either a result of perceptual or attentional blindness depending on the circumstances under which visual awareness was impaired.     

Looking at object-substitution masking in depth and motion: toward a two-object theory of object substitution

When attention is divided, a briefly presented target surrounded by four small dots is difficult to identify when the dots persist beyond target offset, but not when these dots terminate with the target. This object-substitution masking effect likely reflects processes at both the image level and the object level. At the image level, visual contours of the mask make feature extraction difficult. Recent data (Lleras & Moore, 2003) suggest that, at the object level, an object file is created for the target-plus-mask, and this single-object token later morphs into a single-object token containing the mask alone. In the present experiments, we used stimuli presented in 3-D space and apparent motion; the results indicate that object-substitution masking also arises when the mask and the target are represented in two separate object tokens and the mask token interferes with the target token.     

感觉记忆中含语义对象的视觉表征

感觉记忆能够以特征形式构建对视觉对象表面信息的表征, 然而对于具有重要意义的潜在抽象信息, 尚未有研究考察其是否影响感觉记忆的视觉表征。结合掩蔽技术与部分报告法范式考察了感觉记忆的视觉表征中是否包含语义信息。以阿拉伯数字作为目标, 实验1与实验2分别采用正立与倒置的汉字大写数字作为掩蔽刺激, 比较其与白噪音刺激的掩蔽效应。结果显示, 汉字大写数字的掩蔽效应均强于白噪音刺激, 且正立汉字大写数字的掩蔽效果较倒置汉字大写数字更强。实验3采用汉字大写数字与汉字常用字分别作为掩蔽刺激, 结果显示汉字大写数字的掩蔽效果强于汉字常用字。上述结果显示, 刺激间的语义相似性带来了视觉表征冲突, 表明感觉记忆的视觉表征中包含了刺激的语义信息。     

Rapid enumeration within a fraction of a single glance: The role of visible persistence in object individuation capacity

The number of items that can be individuated at a single glance is limited. Here, we investigate object individuation at a higher temporal resolution, in fractions of a single glance. In two experiments involving object individuation we manipulated the duration of visual persistence of the target items with a forward masking procedure. The number of items as well as their stimulus–onset asynchrony (SOA) to the mask was varied independently. The results showed main effects of numerosity and SOA, as well as an interaction. These effects were not caused by a generic reduction of item visibility by the mask. Instead, the SOA manipulation appeared to fractionate the time to access the sensory image. These findings suggest that the capacity limit of 3–4 items found in object individuation is, at least partially, the consequence of the temporal window of access to sensory information.     

Gestalt grouping and common onset masking

A four-dot mask that surrounds and is presented simultaneously with a briefly presented target will reduce a person's ability to identity that target if the mask persists beyond target offset and attention is divided (Enns & Di Lollo, 1997, 2000). This masking effect, referred to as common onset masking, reflects reentrant processing in the visual system and can best be explained with a theory of object substitution (Di Lollo, Enns, & Rensink, 2000). In the present experiments, we investigated whether Gestalt grouping variables would influence the strength of common onset masking. The results indicated that (1) masking was impervious to grouping by form, similarity of color, position, luminance polarity, and common region and (2) masking increased with the number of elements in the masking display.     

What's new in visual masking?

A brief display that is clearly visible when shown alone can be rendered invisible by the subsequent presentation of a second visual stimulus. Several recently described backward masking effects are not predicted by current theories of visual masking, including masking by four small dots that surround (but do not touch) a target object and masking by a surrounding object that remains on display after the target object has been turned off. A crucial factor in both of these effects is attention: almost no masking occurs if attention can be rapidly focused on the target, whereas powerful masking ensues if attention directed at the target is delayed. A new theory of visual masking, inspired by developments in neuroscience, can account for these effects, as well as more traditional masking effects. In addition, the new theory sheds light on related research, such as the attentional blink, inattentional blindness and change blindness.     

Deeper attentional masking by lateral objects in children with autism

Autism spectrum disorder (ASD) is often associated with a detail-oriented perception and overselective attention in visual tasks, such as visual search and crowding. These results were obtained manipulating exclusively the spatial properties of the stimuli: few is known about the spatio-temporal dynamics of visual processing in ASD. In this study we employed an attentional masking (AM) paradigm comparing children with ASD and IQ-matched typically developing (TD) controls. The AM effect refers to an impaired identification of a target followed by a competitive masking object at different proximities in space and time. We found that ASD and TD groups did not differ in the AM effect provoked by the competitive object displayed in the same position of the target. In contrast, children with ASD showed a deeper and prolonged interference than the TD group when the masking object was displayed in the lateral position. These psychophysical results suggest that the inefficient attentional selection in ASD depends on the spatio-temporal interaction between competitive visual objects. These evidence are discussed in the light of the ASD altered neural connectivity hypothesis and the reentrant theory of perception.     

The asymmetry of lateral interference in visual letter identification

Asymmetry of masking refers to the fact that a masking letter placed on the peripheral side of a target in the visual field will interfere more with recognition of the target than will a masking letter placed on the central side of the target. The experiments in this paper show that lateral masking for a pair consisting of a single target and a single mask cannot be entirely explained by processing interference caused by the mask but that masking ]has a component of purely sensory interference. Furthermore, the asymmetry of masking at the sensory level, when all sources of processing interference are eliminated, can be explained in terms of the falloff in acuity from the center to the periphery of the retina. The sensory component of masking is asymmetrical because, with the target at a constant retinal location, the target-plus-mask configuration is, as a whole, more peripherally located with a peripheral mask than a central one, and it is the location of the target-plus-mask configuration that determines performance.     

Size (mostly) doesn’t matter: the role of set size in object substitution masking

Conscious detection and discrimination of a visual target stimulus can be prevented by the presentation a spatially nonoverlapping, but temporally trailing, visual masking stimulus. This phenomenon, known as object substitution masking (OSM), has long been associated with spatial attention, with diffuse attention seemingly being key for the effect to be observed. Recently, this hypothesis has been questioned. We sought to provide a definitive test of the involvement of spatial attention in OSM by using an eight-alternative forced choice task under a range of mask durations, set sizes, and target/distractor spatial configurations. The results provide very little evidence that set size, and thus the distribution of spatial attention, interacts with masking magnitude. These findings have implications for understanding the mechanisms underlying OSM and the relationship between consciousness and attention.     

Visual masking during the attentional blink: tests of the object substitution hypothesis

When 2 masked targets are presented in a rapid sequence, correct identification of the 1st hinders identification of the 2nd. Visual masking of the 2nd target plays a critical role during this 2nd-target deficit, or "attentional blink" (AB). The object substitution hypothesis (B. Giesbrecht & V. Di Lollo, 1998) predicts that late-stage visual processes involved in object substitution mediate masking of the 2nd target during AB, whereby stronger masking should produce a more severe deficit. Six experiments are presented, together testing this hypothesis. Although masking by object substitution was observed, it did not interact with the AB. An alternative hypothesis is proposed stating that mostly early-stage visual processes mediate the masking effects that are critical to the AB.     

The influence of a salient distractor in object-substitution masking

It remains unclear whether a salient distractor directly affects performance accuracy and the perceptual resolution of a target. In order to investigate this issue, the present study employed object substitution masking (OSM) to index perceptual hypothesis testing of a target. Trailing-mask duration of the four-dot mask was varied to investigate how the representation of the masked target decayed over time. Participants responded to the presence of a vertical line on a target ring that was isolated by a four-dot mask while an irrelevant salient distractor was presented in a subset of trials. The results revealed that the salient distractor only impacted performance when the mask and target offset concurrently (Experiment 1) or at short mask durations (Experiment 2). At longer mask durations performance in the distractor present condition was identical to performance in the distractor absent condition, suggesting that involuntary capture of attention did not affect OSM. These results show that the perceptual resolution of a masked target can operate independently of involuntary attentional selection.