Michael Pilling

Is color "categorical perception" really perceptual?

Roberson and Davidoff (2000) found that colorcategorical perception (CP; better cross-category than within-category discrimination) was eliminated by verbal, but not by visual, interference presented during the interstimulus interval (ISI) of a discrimination task. On the basis of this finding, Roberson and Davidoff concluded that CP was mediated by verbal labels, and not by perceptual mechanisms, as is generally assumed. Experiment 1 replicated their results. However, it was found that if the interference type was uncertain on each trial (Experiment 2), CP then survived verbal interference. Moreover, it was found that the target color name could be retained across the ISI even with verbal interference (Experiment 3). We therefore conclude that color CP may indeed involve verbal labeling but that verbal interference does not necessarily prevent it.

Categorical perception of facial expressions: Evidence for a "category adjustment" model

Four experiments probed the nature of categorical perception (CP) for facial expressions. A model based on naming alone failed to accurately predict performance on these tasks. The data are instead consistent with an extension of thecategory adjustment model (Huttenlocher et al., 2000), in which the generation of a verbal code (e.g., “happy”) activated knowledge of the expression category’s range and central tendency (prototype) in memory, which was retained as veridical perceptual memory faded. Further support for a memory bias toward the category center came from a consistently asymmetric pattern of within-category errors. Verbal interference in the retention interval selectively removed CP for facial expressions, under blocked, but not under randomized presentation conditions. However, verbal interference at encoding removed CP even under randomized conditions and these effects were shown to extend even to caricatured expressions, which lie outside the normal range of expression categories.

Categorical effects in visual search for colour

The role of categorization in visual search was studied in 3 colour search experiments where the target was or was not linearly separable from the distractors. The linear separability effect refers to the difficulty of searching for a target that falls between the distractors in CIE colour space (Bauer, Jolicoeur, & Cowan, 1996b). Observers performed nonlinearly separable searches where the target fell between the two types of distractors in CIE colour space. When the target and distractors fell within the same category, search was difficult. When they fell within three distinct categories, response times and search slopes were significantly reduced. The results suggest that categorical information, when available, facilitates search, reducing the linear separability effect.

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.

What Is Being Masked in Object Substitution Masking

Object substitution masking (OSM) is said to occur when a perceptual object is hypothesized that is mismatched by subsequent sensory evidence, leading to a new hypothesized object being substituted for the first. For example, when a brief target is accompanied by a longer lasting display of nonoverlapping mask elements, reporting of target features may be impaired. J. T. Enns and V. Di Lollo (2000) considered it an outstanding question whether OSM masks some or all aspects of a target. The authors report three experiments demonstrating that OSM can selectively affect target features. Participants may be able to detect a target while being unable to report other aspects of it or to report the color but not the orientation of a target (or vice versa). We discuss these findings in relation to two other visual phenomena.

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.

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.

Audiovisual cues and perceptual learning of spectrally distorted speech.

Two experiments investigate the effectiveness of audiovisual (AV) speech cues (cues derived from both seeing and hearing a talker speak) in facilitating perceptual learning of spectrally distorted speech. Speech was distorted through an eight channel noise-vocoder which shifted the spectral envelope of the speech signal to simulate the properties of a cochlear implant with a 6 mm place mismatch. Experiment 1 found that participants showed significantly greater improvement in perceiving noise-vocoded speech when training gave AV cues than when it gave auditory cues alone. Experiment 2 compared training with AV cues with training which gave written feedback. These two methods did not significantly differ in the pattern of training they produced. Suggestions are made about the types of circumstances in which the two training methods might be found to differ in facilitating auditory perceptual learning of speech.

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.