Angus Gellatly

Set size and mask duration do not interact in object substitution masking

Object-substitution masking (OSM) occurs when a mask, such as four dots that surround a brief target item, onsets simultaneously with the target and offsets a short time after the target, rather than simultaneously with it. OSM is a reduction in accuracy of reporting the target with the temporally trailing mask, compared with the simultaneously offsetting mask. It has been thought that OSM occurs only if attention cannot be rapidly focused, or prefocused, on the target location. One line of evidence for this is a reported interaction between target display set size and the duration of the trailing mask. We analyze the evidence for this interaction and suggest it occurs only as an artifact of data being compressed by a ceiling effect. We report six experiments that support this interpretation by showing that the interaction is always absent unless a ceiling effect is induced. We go on to analyze other evidence to support the notion that attention modulates OSM, and argue that in each case, the data either reflect a ceiling effect or can be explained in another way. Our data and our analyses of the existing literature have strong implications for how OSM should be conceptualized.

Exogenous spatial precuing reliably modulates object processing but not object substitution masking

Object substitution masking (OSM) is used in behavioral and imaging studies to investigate processes associated with the formation of a conscious percept. Reportedly, OSM occurs only when visual attention is diffusely spread over a search display or focused away from the target location. Indeed, the presumed role of spatial attention is central to theoretical accounts of OSM and of visual processing more generally (Di Lollo, Enns, & Rensink, Journal of Experimental Psychology: General 129:481–507, 2000). We report a series of five experiments in which valid spatial precuing is shown to enhance the ability of participants to accurately report a target but, in most cases, without affecting OSM. In only one experiment (Experiment 5) was a significant effect of precuing observed on masking. This is in contrast to the reliable effect shown across all five experiments in which precuing improved overall performance. The results are convergent with recent findings from Argyropoulos, Gellatly, and Pilling (Journal of Experimental Psychology: Human Perception and Performance 39:646–661, 2013), which show that OSM is independent of the number of distractor items in a display. Our results demonstrate that OSM can operate independently of focal attention. Previous claims of the strong interrelationship between OSM and spatial attention are likely to have arisen from ceiling or floor artifacts that restricted measurable performance.

Prioritization of looming and receding objects: equal slopes, different intercepts.

Franconeri and Simons (2003) reported that simulated looming objects (marked by a size increase) captured attention, whereas simulated receding objects (marked by a size decrease) did not. This finding has been challenged with the demonstration that receding objects can capture attention when they move in three-dimensional depth. In the present study, we compared the effects of objects that either loomed or receded in depth. The results of two experiments showed that whereas both motion types benefited from attentional prioritization, as judged by their search slopes, looming objects elicited shorter response times (RTs). We conclude that both motion types attract attention during search; however, the RT advantage for looming motion seems to reflect a processing enhancement that occurs outside of selection and is conferred on the basis of motion direction.

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.

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).

Reduced OSM for long duration targets: individuation or items loaded into VSTM?

Typical studies of object substitution masking (OSM) employ a briefly presented search array. The target item is indicated by a cue/mask that surrounds but does not overlap the target and, compared to a common offset control condition, report of the target is reduced when the mask remains present after target offset. Given how little observers are able to report of item arrays that have been presented for several hundred milliseconds (Wolfe, Reinecke, & Brawn, 2006), it might be expected that OSM would also be found if the search array is presented for an extended period before the target is cued by onset of a mask surrounding it. However, Gellatly, Pilling, Carter, and Guest (2010) reported that under these conditions OSM is greatly reduced. This target duration effect could be due to identity information about the search array having been loaded into VSTM during the precue period. Alternatively, it can be understood in terms of target/mask individuation and the object updating account of OSM (Lleras & Moore, 2003). The present article reports three experiments investigating which of these possibilities provides the better explanation of the effect of target duration on OSM. The results support the individuation hypothesis and, thereby, the object updating account of OSM.

Looming motion primes the visuomotor system

A wealth of evidence now shows that human and animal observers display greater sensitivity to objects that move toward them than to objects that remain static or move away. Increased sensitivity in humans is often evidenced by reaction times that increase in rank order from looming, to receding, to static targets. However, it is not clear whether the processing advantage enjoyed by looming motion is mediated by the attention system or the motor system. The present study investigated this by first examining whether sensitivity is to looming motion per se or to certain monocular or binocular cues that constitute stereoscopic motion in depth. None of the cues accounted for the looming advantage. A perceptual measure was then used to examine performance with minimal involvement of the motor system. Results showed that looming and receding motion were equivalent in attracting attention, suggesting that the looming advantage is indeed mediated by the motor system. These findings suggest that although motion itself is sufficient for attentional capture, motion direction can prime motor responses.

Target Visibility in the Standing Wave Illusion: Is Mask—Target Shape Similarity Important?

The perceptibility of a flickering central bar can be dramatically reduced by the presence of two flanking bars presented in counterphase. This phenomenon, known as the ‘standing wave illusion’, has been suggested to involve local edge interactions (Macknik et al, 2000 Proceedings of the National Academy of Sciences of the USA 97 7556–7560). High-level re-entrant mechanisms have also been implicated. Enns (2002, Psychonomic Bulletin & Review 9 489–496) reports an association between the reported viability of the centre bar and its similarity in shape with the flanking bars. We find that this relationship between shape similarity and reported visibility seems to be contingent on the degree of experienced apparent motion. When target duration is shortened, so reducing apparent motion, reports of visibility reflect the amount of abutting contour. In a further experiment we find that luminance discriminations of the centre bar are related to the amount of abutting contour not to shape similarity. This is despite experiment 3 being conducted at stimulus durations for which experiment 2 visibility ratings indicated that shape similarity is important and contour is not. We suggest that this perceived motion may be the factor mediating shape ‘effects’ in the reported visibility task. We propose that the absence of such shape effects in the discrimination task may be because the task provides an objective measure of visibility that is immune to bias from perceived motion. We also speculate that while target luminance information may be immune to masking resulting from perceived motion, it may be subject to masking due to lateral inhibition.

The effect of spatial competition between object-level representations of target and mask on object substitution masking

One of the processes determining object substitution masking (OSM) is thought to be the spatial competition between independent object file representations of the target and mask (e.g., Kahan & Lichtman, 2006). In a series of experiments, we further examined how OSM is influenced by this spatial competition by manipulating the overlap between the surfaces created by the modal completion of the target (an outline square with a gap in one of its sides) and the mask (a four-dot mask). The results of these experiments demonstrate that increasing the spatial overlap between the surfaces of the target and mask increases OSM. Importantly, this effect is not caused by the mask interfering with the processing of the target features it overlaps. Overall, the data indicate, consistent with Kahan and Lichtman, that OSM can arise through competition between independent target and mask representations.

Visual awareness of objects and their colour

At any given moment, our awareness of what we ‘see’ before us seems to be rather limited. If, for instance, a display containing multiple objects is shown (red or green disks), when one object is suddenly covered at random, observers are often little better than chance in reporting about its colour (Wolfe, Reinecke, & Brawn, Visual Cognition, 14, 749–780, 2006). We tested whether, when object attributes (such as colour) are unknown, observers still retain any knowledge of the presence of that object at a display location. Experiments 1–3 involved a task requiring two-alternative (yes/no) responses about the presence or absence of a colour-defined object at a probed location. On this task, if participants knew about the presence of an object at a location, responses indicated that they also knew about its colour. A fourth experiment presented the same displays but required a three-alternative response. This task did result in a data pattern consistent with participants’ knowing more about the locations of objects within a display than about their individual colours. However, this location advantage, while highly significant, was rather small in magnitude. Results are compared with those of Huang (Journal of Vision, 10(10, Art. 24), 1–17, 2010), who also reported an advantage for object locations, but under quite different task conditions.