Academic journal article Psychonomic Bulletin & Review

Object Substitution Masking and the Object Updating Hypothesis

Academic journal article Psychonomic Bulletin & Review

Object Substitution Masking and the Object Updating Hypothesis

Article excerpt

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.

Object substitution masking (OSM) is a recently reported form of visual masking that does not depend on the factors established as important in conventional masking (e.g., the degree of spatial overlap or abutting contour). In OSM, a target can be rendered imperceptible by a mask consisting of just four dots surrounding the target, or, in some circumstances, a single dot presented at a distance from the target location. For OSM to occur, at least two conditions do need to be fulfilled: that the target not be the focus of attention, and that the mask remain present after target offset (Di Lollo, Enns, & Rensink, 2000).

Initial accounts of OSM argued that it arose as a consequence of iterative reentrant exchanges in the cortex that occur as part of the normal processes of the visual system forming a stable representation based on current input. The presence of the trailing mask surrounding the target, it was argued, dramatically reduced the possibility that the stable representation that arises from the iterative exchanges would include the target as well as the mask (Di Lollo et al., 2000). In the original substitution account of OSM, the assumption was that masking consisted of competition for consciousness between two separate object representations. The more recent object updating account of OSM (Enns, Lleras, & Moore, 2009; Lleras & Moore, 2003; Moore & Lleras, 2005) proposes that this competition occurs within a single object representation. This account focuses on the interactions that occur at the object token level of representation, hypothesized midlevel representations considered responsible for maintaining object integrity by linking together the different object attributes over changes in time and space (Kanwisher & Driver, 1992). In the object updating account, OSM is viewed as a consequence of the visual system failing to individuate target and mask as distinct perceptual objects, meaning that the attributes of the target and of the mask are initially bound within the same object token representation. If, under such circumstances, the mask lingers in the display after target offset, the representation will be updated, so the joint target and mask features are overwritten by those of the mask alone, rendering the target features imperceptible.

Key evidence for the object updating account of OSM was presented by Lleras and Moore (2003). In a critical experiment, a target search array was briefly presented around a fixation point. The array was replaced after a variable interstimulus interval (ISI) by a frame consisting of single dots (the masks) presented at locations eccentric from target array items (see the upper portion of Figure 1 for illustration): With a short (17- to 34-msec) ISI, the onset of the mask frame generated a motion signal connecting the dots with the corresponding items in the search array; with the long (216- to 233-msec) ISI, this connecting apparent motion (AM) was not observed. Importantly, masking was found in the short, but not in the long, ISI condition, when measured against a no-mask control condition. …

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