Motion influences Time

Centro de Investigación Básica en Psicología

http://cibpsi.psico.edu.uy

Alejandro Maiche [email protected]

Motion influences Time

Motion and Time: two sides of the same coin

Neural delays problem: perception and awareness emerge once sensory

response to physical events has been transformed by different neural stages. Typically, this implies around 100ms.

Considering that these delays could become life-threatening, it is easy to predict that some sort of compensation mechanism might be evolved.

Many mechanisms have been proposed in order to explain how visual system keep online with moving objects. Most of them appear in the context of Flash-Lag Illusion since one of its possible explanations is a shorter delay for

In a previous research (Maiche et al. 2007) we proposed a pre-activation mechanism, which can be the basis of motion perception and also can allow us to explain the data coming from the flash lag illusion.

Such a mechanism would start low in the processing hierarchy and might be as simple

as possible in order to avoid adding further neurocomputational processing.

The general idea in the context of Flash lag could be represented schematically with this

animation….

In between motion and time:

PRE-ACTIVATION

Facilitated Spot at this moment

In the CIP 2009 (Guimarães) we reasoned that, if pre-activation reduces perceptual latency we should be able to induce

perceptual asynchrony in a synchronous

presentation.

Therefore, we induce perceptual

asynchrony in a two synchronic Gaussian patches display. Consequently, we created a new apparent motion illusion that

emerged from this kind of stimulus configuration.

In order to remember…

Previous reported effects that could be explained by

PRE-ACTIVATION

Our aim is to directly measure the effect of this kind of motion stimulus on the perceptual speed to detect the presence of a static Gaussian patch (RT experiment) and the

Perceived Duration of a static Gaussian patches (PD experiment).

With these ideas in mind….

We show that…

Two simultaneous targets differentially primed generate an illusion of apparent motion. This apparent motion illusion can be either facilitated or reverted depending on which of the targets is preceded by a primer motion.

Reaction Time Experiment

Questions:

1) Is the discrimination of Gaussian patches (above or below the fixation cross) speeded-up by an apparent motion that would collide with Gaussians? (magnitude of the effect of pre-activation for detection)

2) Could we estimate the spatial range where this effect occur? (spatial map of the effect)

We run a simple RT experiment with:

‰8 Participants

‰3 x 6 positions, a within‐subjects design

We run a simple RT experiment with:

‰8 Participants

Did the flash appear above or under the cross?

Results I

Mean RT according to the horizontal and vertical coordinates.

Horizontal dimension (x) was statistically significant F (2,14)= 13.427, p= 0.001.

Vertical dimension (y) was not statistically significant F (5,35)= 1.227, p =0.317. Interaction between both variables was not significant F (10,70)= 9.15, p= 0.524.

Thus, apparent motion speeds up the discrimination in near areas of the motionSo, there is not a clear effect in the vertical dimension, but there seem to be

314 ms

321 ms

331 ms

RTs increases linearly in the horizontal axis

linear trend: F (1,7)= 19.088, p= 0.03

Results II

As if distance from the point where motion stops would be the principal variable that modulate the pre-activation wave.

i. Stimuli located near the motion end-point present lower RTs responses. This could be based on the pre-activation wave generated by the preceded motion, that could determine a lower perceptual delay (at least in the discrimination task that participants performed here).

ii. This facilitation mechanism might be implemented by horizontal connections in the cortex that might spread subthreshold activation which leads to the pre-activation of neurons at future locations of the motion path as previous research have proposed (Bringuier et al., 1999; Jancke et al., 2004; Nijhawan, 2008).

Perceived Duration Experiment

¿Perceived earlier means perceived longer?

• If pre-activation reduces the perceptual delay we can logically think that

those objects affected by pre-activation could be perceived for longer time than those not affected by the pre-activation wave.

• In this experiment, we aim to achieve psychophysical data of perceived

duration of static objects presented near the end-motion point of moving stimuli. We compared the perceived duration of the pre-activated objects with those not pre-activated in a constant stimuli experiment.

For answer this, we start with an experiment using the method of constant stimuli where

subjects have to answer if the second object was longer than first one.

‰9 participants

‰2 experimental conditions: the first Gaussian patch is pre-activated (Yes or No).

‰6 durations of the comparison object (ms): 350; 450; 550; 650; 750; 850

‰Duration of the standard object: 500ms (always appears first)

‰TOTAL: 120 trials per participant.

Questions:

1. Does pre-activation also modulate the perceived duration of static objects? 2. Can we establish some kind of correspondence between the gain of RT

founded in experiment 1 and differences on Perceived Duration depending on the position where static objects would appear?

“The first Gaussian patch is pre-activated” condition :

Perceived Duration Experiment

400 500 600 700 800 0 0.2 0.4 0.6 0.8 1 Comparision time Is the s e c o n d o ne long er? 400 500 600 700 800 0 0.2 0.4 0.6 0.8 1 Comparision time Is the s e c o n d o ne long er? 400 500 600 700 800 0 0.2 0.4 0.6 0.8 1 Comparision time Is the s e c o n d o ne long er?

the first gaussian is pre-activated the firstgaussian is not pre-activated

400 500 600 700 800 0 0.2 0.4 0.6 0.8 1 Comparision time Is the s e c o n d o ne long er? 400 500 600 700 800 0 0.2 0.4 0.6 0.8 1 Comparision time Is the s e c o n d o ne long er? 400 500 600 700 800 0 0.2 0.4 0.6 0.8 1 Comparision time Is the s e c o n d o ne long er? 0.2 0.4 0.6 0.8 1 Is the s e c o n d o ne long er? 0.2 0.4 0.6 0.8 1 Is the s e c o n d o ne long er? 0.2 0.4 0.6 0.8 1 Is the s e c o n d o ne long er?

Individual data of Perceived Duration Experiment

Results I

the first gaussian is pre-activated the first gaussian is not pre-activated

PSE = 595ms PSE = 567ms

Mean estimations of 9 subjects

PSE  PSE 534 586 475 585 609 650 635 646 514 535 546 534 577 577 656 597 625 687

Results II

• In the condition of “the first Gaussian is NOT pre-activated” the PSE is longer

than physical duration of first Gaussian (567ms). This means that first object is overestimated even without any pre-activation effect.

This might be related with the usual tendency to overestimate the first of two successive intervals when both are relatively short (Block;1994; Kanai et al, 2009).

• In the condition of “the first Gaussian IS pre-activated” the PSE is 595ms. This

is 28 ms more than when the “Gaussian is not pre-activated” and this could be related to the speeded-up detection time that we found in experiment 1

Conclusions

• According to the spatial facilitation hypothesis, apparent moving stimuli would

facilitate the detection of targets located ahead of the moving stimuli (experiment 1).

• Our results revealed that RTs were lower for targets located near that

end-point of the motion allowing a rough estimation of the size and form of the spatial facilitated window.

• Stimuli presented in the area of spatial facilitation were perceived longer

than stimuli not affected by the pre-activation wave (Experiment 2). The magnitude of the overestimation seems to roughly correspond with the gain of time in the discrimination task (Experiment 1). However, the relationship between both perceptual processes (discrimination and duration estimation) might not be so simple.

• These results would support the idea that spatial facilitation generated by

motion could be in the basis of many low level perceptive process (at least discrimination and time estimation).

Thanks...

Graciès…

Fourth Iberian Conference on Perception Palma  6‐8 Julio 2011

Fourth Iberian Conference on Perception

Palma  6‐8 Julio 2011

Alejandro Maiche; Ana Pires y Leonel Gómez (UAB, UdelaR)