Perception

To estimate intrinsic descriptors of objects in the environment, effective biological vision systems must ‘discount’ extrinsic image properties that arise from changes in viewing conditions. In particular, to estimate the reflectance of surfaces, human vision must discount, or ‘take account of’, likely differences in the illumination of surfaces between one image region and another. If human vision possesses any significant degree of lightness constancy, then we would expect a target perceived to be in low illumination to appear lighter than an identical target perceived to be in higher illumination. In this paper, I present lightness illusions that run directly counter to this expectation. I suggest that mid-level and higher-level factors such as image junction structure and perceived illumination and transparency, are ineffective for generating strong lightness illusions on their own, and that these factors are not ‘stronger’ than luminance contrast in determining lightness. I discuss the implications of these results for current models of lightness perception. I also suggest a statistical justification for the highest-luminance anchoring rule for lightness.

Simultaneous lightness contrast is stronger when the dark and light backgrounds of the classic display (where one of the targets is an increment and the other is a decrement) are replaced by articulated fields of equivalent average luminances. Although routinely attributed to articulation per se, this effect may simply result from the increase in highest luminance in the light articulated, vs plain, background; by locally darkening the decremental target, such an increase would amplify the difference between the targets. We disentangled the effects of highest luminance and articulation by measuring, separately, the magnitude of lightness contrast on dark and light plain and articulated backgrounds. We found that highest luminance and articulation contribute separately to the final illusion.

The position of a moving object is often mislocalised in the direction of movement. At the input stage of visual processing, the position of a moving object should still be represented veridically, whereas it should become closer to the mislocalised position at a later processing stage responsible for positional judgment. Here, we show that visual transients expose the veridical position of a moving object represented in early visual areas. For example, when a ring is flashed on a moving bar, the part of the bar within the ring is perceived at the veridical position, whereas the part outside the ring is perceived to be ahead of the ring as in the flash-lag effect. Our observations suggest that a filling-in process is triggered at the edges of the flash. This indicates that, in early cortical areas, moving objects are still represented at their veridical positions, and the perceived location is determined by the higher visual areas.

Color assimilation with bichromatic contours was quantified for spatial extents ranging from von Bezold-type color assimilation to the watercolor effect. The magnitude and direction of assimilative hue change was measured as a function of the width of a rectangular stimulus. Assimilation was quantified by hue cancellation. Large hue shifts were required to null the color of stimuli ≤9.3 min of arc in width, with an exponential decrease for stimuli increasing up to 7.4 deg. When stimuli were viewed through an achromatizing lens, the magnitude of the assimilation effect was reduced for narrow stimuli, but not for wide ones. These results demonstrate that chromatic aberration may account, in part, for color assimilation over small, but not large, surface areas.

How do humans combine the velocity information from two moving gratings (plaids) to detect pattern motion direction? We are still unable to answer this question. The ‘intersection of constraints’ rule (IOC—Adelson and Movshon, 1982 Nature 300 523–525), and the ‘vector average’ rule (VA—Wilson et al, 1992 Visual Neuroscience 9 79–97) have both been supported by results in the plaid literature, but could these results be predicted by a ‘squaring’ nonlinearity that now forms part of several influential spatiotemporal energy models (Wilson et al 1992, loco cit.; Lu and Sperling, 1995 Vision Research 35 2697–2722; Simoncelli and Heeger, 1998 Vision Research 38 743–761)? Spatiotemporal energy in these models predicts directions other than those predicted by standard spatiotemporal energy models and may underlie the results that support the combination rules. The two combination rules and predictions from ‘squaring’ were tested under identical conditions. In the first three experiments a plaid was randomly presented in one of 45 different orientations, and observers were asked to remember the direction. The stimulus was then replaced by an oriented line indicating the direction predicted by one of the hypotheses. The observer was unaware which hypothesis had generated the line and was asked to make a same/different judgment. Results showed that the ‘squaring’ hypothesis was better at predicting perceived direction than either the IOC or VA.

In our natural viewing, we notice that objects change their locations across space and time. However, there has been relatively little consideration of the role of motion information in the construction and maintenance of object representations. We investigated this question in the context of the multiple object tracking (MOT) paradigm, wherein observers must keep track of target objects as they move randomly amid featurally identical distractors. In three experiments, we observed impairments in tracking ability when the motions of the target and distractor items shared particular properties. Specifically, we observed impairments when the target and distractor items were in a chasing relationship or moved in a uniform direction. Surprisingly, tracking ability was impaired by these manipulations even when observers failed to notice them. Our results suggest that differentiable trajectory information is an important factor in successful performance of MOT tasks. More generally, these results suggest that various types of common motion can serve as cues to form more global object representations even in the absence of other grouping cues.

The spatiotemporal pattern projected by a moving object is specific to that object, as it depends on both the shape and the dynamics of the object. Previous research has shown that observers learn to make use of this spatiotemporal signature to recognize dynamic faces and objects. In two experiments, we assessed the extent to which the structural similarity of the objects and the presence of spatiotemporal noise affect how these signatures are learned and subsequently used in recognition. Observers first learned to identify novel, structurally distinctive or structurally similar objects that rotated with a particular motion. At test, each learned object moved with its studied motion or with a non-studied motion. In the non-studied motion condition we manipulated either dynamic information alone (experiment 1) or both static and dynamic information (experiment 2). Across both experiments we found that changing the learned motion of an object impaired recognition performance when 3-D shape was similar or when the visual input was noisy during learning. These results are consistent with the hypothesis that observers use learned spatiotemporal signatures and that such information becomes progressively more important as shape information becomes less reliable.

When observers are asked to identify the global and local dimensions of hierarchical forms, their responses are typically faster when the dimensions are consistent rather than inconsistent. This effect, which we refer to as the dimensional consistency effect, has been demonstrated numerous times in paradigms requiring responses to a single dimension. However, most hypotheses regarding dimensional consistency effects address the simultaneous perception of both dimensions, and the manner in which the information about these dimensions may (or may not) ‘interact’. Most explanations of the dimensional consistency effect attribute the effect to perceptual influences. The present study uses the constructs of general recognition theory (Ashby and Townsend, 1986 Psychological Review 93 154–179) to represent the source of the effect in terms of both perceptual and decisional influences. In addition, a complete identification response paradigm was used to collect data on the simultaneous perception of both global and local dimensions of hierarchical forms. Analyses of multidimensional signal detection measures and fits of parametric models of the perceptual space were used to guide inferences, with all sources of evidence pointing to both perceptual and decisional influences.

The role of configural information in gender categorisation was studied by aligning the top half of one face with the bottom half of another. The two faces had the same or different genders. Experiment l shows that participants were slower and made more errors in categorising the gender in either half of these composite faces when the two faces had a different gender, relative to control conditions where the two faces were nonaligned or had the same gender. This result parallels the composite effect for face recognition (Young et al, 1987 Perception 16 747–759) and facial-expression recognition (Calder et al, 2000 Journal of Experimental Psychology: Human Perception and Performance 26 527–551). Similarly to responses to face identity and expression, the composite effect on gender discrimination was disrupted by inverting the faces (experiment 2). Both experiments also show that the composite paradigm is sensitive to general contextual interference in gender categorisation.

Font tuning (FT) occurs when observers recognize a sequence of letters presented in the same font faster than in different fonts (Sanocki 1987, 1988 Journal of Experimental Psychology: Human Perception and Performance 13 267–278; 14 472–480). Here, we test the hypothesis that FT is associated with expertise with a specific writing system. We developed a systematic search task allowing the measurement of FT over a large number of letters and generalized the finding of FT from English readers viewing Roman letters to Chinese readers viewing Chinese characters. Non-Chinese readers did not show evidence of FT for Chinese characters in this search task. We also used a simpler 3-letter identification task to directly compare novice and expert readers, and to explore FT for different aspects of font such as fill, slant, and aspect ratio. We found that experts tune to aspect ratio but not to the other font changes. These findings reveal that letters are not processed visually in the same manner as shapes, and suggest an explanation for the cortical specialization obtained in the visual system for letters.

Visuospatial performance, assessed with the new, group-administered Judgment of Line Angle and Position test (JLAP-13), varied with sex and mathematical competence in a group of adolescents. The JLAP-13, a low-level perceptual task, was modeled after a neuropsychological task dependent upon functioning of the posterior region of the right hemisphere [Benton et al, 1994 Contributions to Neuropsychological Assessment: A Clinical Manual (New York: Oxford University Press)]. High-school boys (N = 52) performed better than girls (N = 62), with a large effect for sex (d= 1.11). Performance increased with mathematical competence, but the sex difference did not vary significantly across different levels of mathematics coursework. On the basis of earlier work, it was predicted that male, but not female, performance in line judgment would decline with disruptions to task geometry (page frame), and that the sex difference would disappear with disruptions to geometry. These predictions were supported by a number of univariate and sex-specific analyses, although an omnibus repeated-measures analysis did not detect the predicted interaction, most likely owing to limitations in power. Thus, there is partial support for the notion that attentional predispositions or strategies may contribute to visuospatial sex differences, with males more likely than females to attend to, and rely upon, internal or external representations of task geometry. Additional support for this hypothesis may require development of new measures or experimental manipulations with more powerful geometrical disruptions.

When the right index fingertip of twelve subjects was moved across a cold (15°C) tile by a machine (passive-guided condition), the subjects rated the temperature of the tile as being colder than when they moved the finger across the stimulus themselves (active condition). Results confirmed that active movements were associated with an attenuation of ‘coldness’. When these findings are considered alongside those of earlier experiments (see VanDoorn et al, 2005 Perception 34 231–236), it may be concluded that intentionality of movement plays some role in this attenuation.