Biomedical subjects

Joan López-Moliner

Publications and source records attributed to Joan López-Moliner.

9 recordsLinked to original sources

PubMed2007

Absence of flash-lag when judging global shape from local positions.

When a flash is presented aligned with a moving stimulus, the former is perceived to lag behind the latter (the flash-lag effect). We study whether this mislocalization occurs when a positional judgment is not required, but a veridical spatial relationship between moving and flashed stimuli is needed to perceive a global shape. To do this, we used Glass patterns that are formed by pairs of correlated dots. One dot of each pair was presented moving and, at a given moment, the other dot of each pair was flashed in order to build the Glass pattern. If a flash-lag effect occurs between each pair of dots, we expect the best perception of the global shape to occur when the flashed dots are presented before the moving dots arrive at the position that physically builds the Glass pattern. Contrary to this, we found that the best detection of Glass patterns occurred for the situation of physical alignment. This result is not consistent with a low-level contribution to the flash-lag effect.

Form Perception↗

PubMed2006

Perceptual asynchrony between color and motion with a single direction change.

When a stimulus repeatedly and rapidly changes color (e.g., between red and green) and motion direction (e.g., upwards and downwards) with the same frequency, it was found that observers were most likely to pair colors and motion directions when the direction changes lead the color changes by approximately 80 ms. This is the color-motion asynchrony illusion. According to the differential processing time model, the illusion is explained because the neural activity leading to the perceptual experience of motion requires more time than that of color. Alternatively, the time marker model attributes the misbinding to a failure in matching different sorts of changes at rapid alternations. Here, running counter to the time marker model, we demonstrate that the illusion can arise with a single direction change. Using this simplified version of the illusion we also show that, although some form of visual masking takes place between colors, the measured asynchrony genuinely reflects processing time differences.

Color Perception↗

PubMed2006

The flash-lag effect is reduced when the flash is perceived as a sensory consequence of our action.

The flash-lag effect (FLE) is defined as an error in localization that consists of perceiving a flashed object to lag behind a moving one when both are presented in physical alignment. Previous studies have addressed the question if it is the predictability of the flash, or the moving object, that modulates the amount of the error. However, the case when the flash is self-generated, and hence can be internally predicted, has not yet been addressed. In Experiment 1, we compare four conditions: flash unpredictable, flash externally predicted by a beep, flash internally generated (and predicted) by pressing a key, and flash triggered by a key press but temporally unpredictable. The FLE was significantly reduced only when the flash was internally predictable. In Experiment 2, we rule out the possibility that the reduction of the FLE was due to the use of the key press as a temporal marker. We conclude that when the flash is perceived as a sensory consequence of our own action, its detection can be speeded up, thereby resulting in a reduction of the FLE. A third experiment supports this interpretation. The mechanism by virtue of which the detection is accelerated could be related to efferent signals from motor areas predicting the sensory consequences of our actions.

Attention↗

PubMed2005

Determining whether a ball will land behind or in front of you: not just a combination of expansion and angular velocity.

We propose and evaluate a source of information that ball catchers may use to determine whether a ball will land behind or in front of them. It combines estimates for the ball's horizontal and vertical speed. These estimates are based, respectively, on the rate of angular expansion and vertical velocity. Our variable could account for ball catchers' data of Oudejans et al. [The effects of baseball experience on movement initiation in catching fly balls. Journal of Sports Sciences, 15, 587-595], but those data could also be explained by the use of angular expansion alone. We therefore conducted additional experiments in which we asked subjects where simulated balls would land under conditions in which both angular expansion and vertical velocity must be combined for obtaining a correct response. Subjects made systematic errors. We found evidence for the use of angular velocity but hardly any indication for the use of angular expansion. Thus, if catchers use a strategy that involves combining vertical and horizontal estimates of the ball's speed, they do not obtain their estimates of the horizontal component from the rate of expansion alone.

Attention↗

PubMed2004

Components of motion perception revealed: two different after-effects from a single moving object.

If motion that one has been looking at for some time suddenly stops, or if one shifts one's gaze to a static object, one will see motion in the opposite direction: the motion after-effect. If two transparent surfaces move with different speeds in different directions, then the direction of the motion after-effect will depend on the test pattern. For such transparent surfaces both the local motion and the global percept have two components. When looking at a normal moving object, there is only one perceived global motion. However, we know that locally there can be considerable ambiguity (the aperture problem). Does one adapt to all the local components, including those that one does not perceive, or only to the perceived global motion? We designed a stimulus that is perceived to be a fast rotating object, but also has a slow local radial component of motion. By selecting an appropriate test pattern we could either get a radial or a rotating motion after-effect. Thus we show that adaptation to motion must (also) occur at a stage at which local motions have not yet been integrated to give a unified percept.

Adaptation, Physiological↗

PubMed2003

Spatial interference and response control in sequence learning: the role of explicit knowledge.

In several sequence learning studies it has been suggested that response control shifts from the stimuli to some internal representation (i.e., motor program) through the learning process. The main questions addressed in this paper are whether this control shift is related to explicit knowledge and whether the formation of these internal representations depends on the stimulus attributes. In one experiment we compared the learning of a response sequence triggered by either spatial location or location symbol (left-right) by using a serial response task (SRT). Symbols were presented at either a centered or random location. The results showed that in the symbolic conditions the shift of response control correlated with the emergence of explicit knowledge. Only participants with complete explicit knowledge seemed to learn the sequence structure beyond probabilistic information (response time "RT" did not depend on the frequency of the response). Moreover, these participants were able to overcome, when needed, spatial interference (RT was the same for both spatially corresponding and non-corresponding trials). However, when spatial location was relevant, RT was always faster, especially for more frequent responses. These results suggest that the relevant stimulus dimension (location or symbol) seems to engage different sequence learning mechanisms.

Adult↗

PubMed2003

Similar effects of a motion-in-depth illusion on manual tracking and perceptual judgements.

We previously demonstrated that changing the apparent extent of a target's apparent motion-in-depth, by manipulating pictorial depth cues in the surrounding, affected perceptual judgements and manual pursuit to the same extent. Here, we investigated whether a different manipulation of the extent of motion (expanding and contracting the object itself) also has the same effect on both tasks. Objects were presented that changed in size as they moved on an elliptical path. The size was related to the object's position in the sagittal plane, suggesting additional motion in depth; therefore the illusion was expected to affect sagittal measures for both perception and action. We measured manual tracking and perceptual judgements of the lateral and sagittal extents of the object's elliptical trajectories. A significant correlation was found across subjects between the effect of the illusion on the perceptual and the motor task. As expected, the illusion only had a significant influence on the sagittal dimension. The size of this illusory effect was equal for perception and action.

Cues↗

PubMed2003

Comparing the sensitivity of manual pursuit and perceptual judgments to pictorial depth effects.

We examined whether a pictorial depth illusion influences the manual pursuit of a moving dot to the same extent that it influences the dot's apparent displacement. Fourteen subjects performed two tasks. In one case, they used their unseen hand to track a dot that moved on an elliptical path. In the other, they first watched the dot move on the same path, and then set an ellipse to match the shape of the dot's path. The illusion influenced the two tasks to the same extent, suggesting that the visual information processing is the same for the two tasks.

Attention↗

PubMed2002

Speed of response initiation in a time-to-contact discrimination task reflects the use of eta.

Avoiding collisions and making interceptions seem to require an organism to estimate the time that will elapse before an object will arrive to the point of observation (time-to-contact). The most outstanding account for precise timing has been the tau hypothesis. However, recent studies demonstrate that tau is not the only source of information in judging time-to-contact. By measuring reaction time in a time-to-contact discrimination task, we show that the eta function, which is a specific combination of optical size and rate of expansion, explains both accuracy and the observed RT pattern. The results conform to the hypothesis that the observers initiate the response when eta reaches a response threshold value.

Depth Perception↗