Lisa Scocchia

What’s “up”? Working memory contents can bias orientation processing

We explored the interaction between the processing of a low-level visual feature such as orientation and the contents of working memory (WM). In a first experiment, participants memorized the orientation of a Gabor patch and performed two subsequent orientation discriminations during the retention interval. The WM stimulus exerted a consistent repulsive effect on the discrimination judgments: participants were more likely to report that the discrimination stimulus was rotated clockwise compared to the oblique after being presented with a stimulus that was tilted anti-clockwise from the oblique. A control condition where participants attended to the Gabor patch but did not memorize it, showed a much reduced effect. The repulsive effect was stable across the two discriminations in the memory condition, but not in the control condition, where it decayed at the second discrimination. In a second experiment, we showed that the greater interference observed in the WM condition cannot be explained by a difference in cognitive demands between the WM and the control condition. We conclude that WM contents can bias perception: the effect of WM interference is of a visual nature, can last over delays of several seconds and is not disrupted by the processing of intervening visual stimuli during the retention period.

Visual Working Memory Contents Bias Ambiguous Structure from Motion Perception

The way we perceive the visual world depends crucially on the state of the observer. In the present study we show that what we are holding in working memory (WM) can bias the way we perceive ambiguous structure from motion stimuli. Holding in memory the percept of an unambiguously rotating sphere influenced the perceived direction of motion of an ambiguously rotating sphere presented shortly thereafter. In particular, we found a systematic difference between congruent dominance periods where the perceived direction of the ambiguous stimulus corresponded to the direction of the unambiguous one and incongruent dominance periods. Congruent dominance periods were more frequent when participants memorized the speed of the unambiguous sphere for delayed discrimination than when they performed an immediate judgment on a change in its speed. The analysis of dominance time-course showed that a sustained tendency to perceive the same direction of motion as the prior stimulus emerged only in the WM condition, whereas in the attention condition perceptual dominance dropped to chance levels at the end of the trial. The results are explained in terms of a direct involvement of early visual areas in the active representation of visual motion in WM.

The influence of facing direction on the haptic identification of two-dimensional raised pictures.

It has been hypothesized (Lederman et al, 1990 Perception & Psychophysics 47 54–64) that sighted people adopt a visual translation process when attempting to identify 2-D raised images by touch—they employ a visual image as a mediator between haptic sensory information and the object representation. If this hypothesis is correct, the performance in identifying pictures by touch (with eyes closed) ought to be better when the head is facing the picture than when facing in a very different direction. In this study, thirty-six blindfolded participants were required to identify raised pictures of common objects with their head facing either in the same direction as the raised picture or in an orthogonal direction. Identification performance was measured in terms of accuracy and response latencies. Overall, participants were more accurate and faster when their heads faced in the same direction as the picture. This finding is discussed in terms of spatial congruency between haptic representations of pictures and visual (or spatial) imagery created during exploration of haptic pictures.

Observer's control of the moving stimulus increases the flash-lag effect

The flash-lag effect (FLE) consists in perceiving a briefly presented stationary stimulus to lag behind an aligned moving stimulus. This study investigates the effects of actively controlling the moving stimulus. By means of a robotic arm, observers continuously moved a dot along a circular trajectory, and a flash was displayed closely at unpredictable times. In two experiments, we found that the FLE was larger when participants controlled the moving stimulus, compared to a computer-controlled condition. Two control conditions tested the possibility that the observed modulation of the FLE was due to visuo-spatial attention or dual-task factors. This study provides evidence that the motor system interacts with and possibly speeds up the processing of a moving visual stimulus when the observer controls its movement.

Differential effects of visual attention and working memory on binocular rivalry

The investigation of cognitive influence on binocular rivalry has a long history. However, the effects of visual WM on rivalry have never been studied so far. We examined top-down modulation of rivalry perception in four experiments to compare the effects of visual WM and sustained selective attention: In the first three experiments we failed to observe any sustained effect of the WM content; only the color of the memory probe was found to prime the initially dominant percept. In Experiment 4 we found a clear effect of sustained attention on rivalry both in terms of the first dominant percept and of the overall dominance when participants were involved in a tracking task. Our results provide an example of dissociation between visual WM and selective attention, two phenomena which otherwise functionally overlap to a large extent. Furthermore, our study highlights the importance of the task employed to engage cognitive resources: The observed perceptual epiphenomena of binocular rivalry are indicative of visual competition at an early stage, which is not affected by WM but is still susceptible to attention influence as long as the observer’s attention is constrained to one of the two rival images via a specific concomitant task.

Spatial Alignment and Response Hand in Geometric and Motion Illusions

Perception of visual illusions is susceptible to manipulation of their spatial properties. Further, illusions can sometimes affect visually guided actions, especially the movement planning phase. Remarkably, visual properties of objects related to actions, such as affordances, can prime more accurate perceptual judgements. In spite of the amount of knowledge available on affordances and on the influence of illusions on actions (or lack of thereof), virtually nothing is known about the reverse: the influence of action-related parameters on the perception of visual illusions. Here, we tested a hypothesis that the response mode (that can be linked to action-relevant features) can affect perception of the Poggendorff (geometric) and of the Vanishing Point (motion) illusion. We explored the role of hand dominance (right dominant versus left non-dominant hand) and its interaction with stimulus spatial alignment (i.e., congruency between visual stimulus and the hand used for responses). Seventeen right-handed participants performed our tasks with their right and left hands, and the stimuli were presented in regular and mirror-reversed views. It turned out that the regular version of the Poggendorff display generates a stronger illusion compared to the mirror version, and that participants are less accurate and show more variability when they use their left hand in responding to the Vanishing Point. In summary, our results show that there is a marginal effect of hand precision in motion related illusions, which is absent for geometrical illusions. In the latter, attentional anisometry seems to play a greater role in generating the illusory effect. Taken together, our findings suggest that changes in the response mode (here: manual action-related parameters) do not necessarily affect illusion perception. Therefore, although intuitively speaking there should be at least unidirectional effects of perception on action, and possible interactions between the two systems, this simple study still suggests their relative independence, except for the case when the less skilled (non-dominant) hand and arguably more deliberate responses are used.

When Geometry Constrains Vision: Systematic Misperceptions within Geometrical Configurations

How accurate are we in reproducing a point within a simple shape? This is the empirical question we addressed in this work. Participants were presented with a tiny disk embedded in an empty circle (Experiment 1 and 3) or in a square (Experiment 2). Shortly afterwards the disk vanished and they had to reproduce the previously seen disk position within the empty shape by means of the mouse cursor, as accurately as possible. Several loci inside each shape were tested. We found that the space delimited by a circle and by a square is not homogeneous and the observed distortion appears to be consistent across observers and specific for the two tested shapes. However, a common pattern can be identified when reproducing geometrical loci enclosed in a shape: errors are shifted toward the periphery in the region around the center and toward the center in the region nearby the edges. The error absolute value declines progressively as we approach an equilibrium contour line between the center and the outline of the shape where the error is null. These results suggest that enclosing an empty space within a shape imposes an organization to it and warps its metrics: not only the perceived loci inside a shape are not the same as the geometrical loci, but they are misperceived in a systematic way that is functional to the correct identification of the center of the shape. Eye movements recordings (Experiment 3) are consistent with this interpretation of the data.

Author Correction: Children’s first handwriting productions show a rhythmic structure

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.

Repulsive Serial Effects in Visual Numerosity Judgments

We investigated how the approximate perceived numerosity of ensembles of visual elements is modulated by the numerosity of previously viewed ensembles depending on whether the first ensemble is held in visual working memory or not. We show that the numerosity of the previously seen ensemble has a repulsive effect, that is, a stimulus with high numerosity induces an underestimation of the following one and vice versa. This repulsive effect is present regardless of whether the first stimulus is memorized or not. While subtle changes of the experimental paradigm can have major consequences for the nature of interstimulus dependencies in perception, generally speaking the fact that we found such effects in a visual numerosity estimation task confirms that the process by which human observers produce estimates of the number of elements bears analogies to the processes that lead to the perception of visual dimensions such as orientation.

The haptic and the visual flash-lag effect and the role of flash characteristics

When a short flash occurs in spatial alignment with a moving object, the moving object is seen ahead the stationary one. Similar to this visual “flash-lag effect” (FLE) it has been recently observed for the haptic sense that participants judge a moving hand to be ahead a stationary hand when judged at the moment of a short vibration (“haptic flash”) that is applied when the two hands are spatially aligned. We further investigated the haptic FLE. First, we compared participants’ performance in two isosensory visual or haptic conditions, in which moving object and flash were presented only in a single modality (visual: sphere and short color change, haptic: hand and vibration), and two bisensory conditions, in which the moving object was presented in both modalities (hand aligned with visible sphere), but the flash was presented only visually or only haptically. The experiment aimed to disentangle contributions of the flash’s and the objects’ modalities to the FLEs in haptics versus vision. We observed a FLE when the flash was visually displayed, both when the moving object was visual and visuo-haptic. Because the position of a visual flash, but not of an analogue haptic flash, is misjudged relative to a same visuo-haptic moving object, the difference between visual and haptic conditions can be fully attributed to characteristics of the flash. The second experiment confirmed that a haptic FLE can be observed depending on flash characteristics: the FLE increases with decreasing intensity of the flash (slightly modulated by flash duration), which had been previously observed for vision. These findings underline the high relevance of flash characteristics in different senses, and thus fit well with the temporal-sampling framework, where the flash triggers a high-level, supra-modal process of position judgement, the time point of which further depends on the processing time of the flash.