Voluntary attention increases the phenomenal length of briefly flashed lines Masin S. C. University of Padua

The study reported here is about the possible effect of attention on the phenomenal length of briefly flashed lines.

A briefly flashed line is, for example, a black line as this:

The study reported here is about the possible effect of attention on the phenomenal length of briefly flashed lines. A briefly flashed line is, for example, a black line as this:

The study reported here is about the possible effect of attention on the phenomenal length of briefly flashed lines. A briefly flashed line is, for example, a black line as this:

There have been many attempts at determining whether attention affects the phenomenal length of briefly presented lines.

However, although previous studies claim that attention influences phenomenal length, in reality the results of these studies do not allow one to distinguish the effect of attention on phenomenal length from the effect of attention on remembered length.

There have been many attempts at determining whether attention affects the phenomenal length of briefly presented lines. However, although previous studies claim that attention influences phenomenal length, in reality the results of these studies do not allow one to distinguish the effect of attention on phenomenal length from the effect of attention on remembered length. The reason for this confusion is the following.

For example, P RINZMETAL and W ILSON (1997) studied the effect of attention on line length by presenting a fixation cross as this:

The fixation cross was followed by a stimulus like this:

(The duration of the stimulus was about 50 msec)

The fixation cross was followed by a stimulus like this: Subjects had the task to detect a letter in this matrix. (The duration of the stimulus was about 50 msec)

The fixation cross was followed by a stimulus like this: Subjects had the task to detect a letter in this matrix. (The duration of the stimulus was about 50 msec) This test line was simultaneous with the matrix or appeared 0.5 sec after the matrix.

The fixation cross was followed by a stimulus like this: Subjects had the task to detect a letter in this matrix. (The duration of the stimulus was about 50 msec) This test line was simultaneous with the matrix or appeared 0.5 sec after the matrix. Thus the test line received more attention when it appeared after the matrix.

Several seconds after the test line and the matrix had disappeared, subjects varied the length of a comparison line such as this…

Several seconds after the test line and the matrix had disappeared, subjects varied the length of a comparison line such as this…

Several seconds after the test line and the matrix had disappeared, subjects varied the length of a comparison line such as this… …to make it equal to the length of the test line.

Several seconds after the test line and the matrix had disappeared, subjects varied the length of a comparison line such as this… …to make it equal to the length of the test line.

Several seconds after the test line and the matrix had disappeared, subjects varied the length of a comparison line such as this… …to make it equal to the length of the test line. Clearly, the comparison line was compared with the memory of the test line, not with the phenomenal length of the test line, because the comparison occurred…

Several seconds after the test line and the matrix had disappeared, subjects varied the length of a comparison line such as this… …to make it equal to the length of the test line. Clearly, the comparison line was compared with the memory of the test line, not with the phenomenal length of the test line, because the comparison occurred…

Several seconds after the test line and the matrix had disappeared, subjects varied the length of a comparison line such as this… …to make it equal to the length of the test line. Clearly, the comparison line was compared with the memory of the test line, not with the phenomenal length of the test line, because the comparison occurred…

P RINZMETAL and W ILSON (1997) found that the adjusted comparison line was longer when the test line received more attention.

However, as we have just seen, this effect of attention could well have been a memory effect rather than a phenomenal effect. P RINZMETAL and W ILSON (1997) found that the adjusted comparison line was longer when the test line received more attention.

However, as we have just seen, this effect of attention could well have been a memory effect rather than a phenomenal effect. To resolve this issue, the following study was carried out. P RINZMETAL and W ILSON (1997) found that the adjusted comparison line was longer when the test line received more attention.

In the following experiment, a white fixation cross was presented on each trial.

The subjects were instructed to direct their attention on the side of the cross indicated by the blackening of one arm.

The subjects were instructed to direct their attention on the side of the cross indicated by the blackening of one arm. For example…

on the left For example… The subjects were instructed to direct their attention on the side of the cross indicated by the blackening of one arm.

on the right For example… The subjects were instructed to direct their attention on the side of the cross indicated by the blackening of one arm.

For example… on the top The subjects were instructed to direct their attention on the side of the cross indicated by the blackening of one arm.

at the bottom For example… The subjects were instructed to direct their attention on the side of the cross indicated by the blackening of one arm.

The test line and the comparison line had a width of 1 pixel and a length of 50 mm. They were presented simultaneously for 50 msec

The test line and the comparison line had a width of 1 pixel and a length of 50 mm. They were presented simultaneously for 50 msec vertically

The test line and the comparison line had a width of 1 pixel and a length of 50 mm. They were presented simultaneously for 50 msec vertically or horizontally.

The test line and the comparison line were presented few milliseconds before or after one arm of the cross turned black.

For example the test line and the comparison line were presented like this…

For example the test line and the comparison line were presented like this…

For example the test line and the comparison line were presented like this…

For example the test line and the comparison line were presented like this…

For example the test line and the comparison line were presented like this… By definition, the test line was the line indicated by the black arm of the cross.

For example the test line and the comparison line were presented like this… By definition, the test line was the line indicated by the black arm of the cross. In the case just shown, subjects had to report whether the test line (located on the left) was longer or shorter than the comparison line (located on the right).

Let this line represent the time axis.

This arrow represents the moment when one arm of the fixation cross turnes black (that is, the moment when the cue occurs).

This solid line represents the duration of the test line (50 msec).

This arrow represents the moment when attention is deployed.

This arrow represent the moment when attention is deployed. C ARLSON, H OGENDOORN, and V ERSTRATEN (2006) have recently shown that voluntary attention is deployed about 240 msec from when a cue occurs.

In the present experiment, the cue was presented with different delays.

We can make the following predictions:

If the effect of attention is

We can make the following predictions: phenomenal If the effect of attention is

We can make the following predictions: Strong effect If the effect of attention is phenomenal

We can make the following predictions: Strong effect Small or no effect If the effect of attention is phenomenal

We can make the following predictions: Strong effect Small or no effect If the effect of attention is phenomenalmemory

We can make the following predictions: Strong effect Small or no effect Some effect If the effect of attention is phenomenalmemory

We can make the following predictions: Strong effect Small or no effect Some effect The same or stronger effect If the effect of attention is phenomenalmemory

PLPL

PLPL

PLPL PRPR

PLPL PRPR

PLPL PRPR

PLPL PRPR If attention has no effect on line length than one expects that P L = 1 – P R

PLPL PRPR If attention has no effect on line length than one expects that P L = 1 – P R Instead, if attention increases line length than one expects that P L > 1 – P R

Results for:

Results for: vertical lines PLPL PRPR

Results for: vertical lines horizontal lines PLPL PRPR PAPA PBPB

I NTERPRETATION OF R ESULTS ( 1 ) There is large evidence that lines appearing with abrupt onset expand perceptually during the first half a second of their presentation. This evidence shows that lines presented abruptly activate motion detectors (that motion detectors are activated is proved by Holt-Hansen’s finding that when a briefly flashed line is presented repeatedly with short interstimulus intervals, subjects perceive a propeller-like rotation of the line). ( 2 ) There is large evidence that the amplitude of the neural responses produced by a stimulus is increased when attention is directed to the stimulus and is reduced when attention is directed outside the stimulus. ( 3 ) Consequently, in the present study, when attention was directed to one line of a stimulus and was simultaneously diverted from the other line of the same stimulus, the amplitude of neural responses of motion detectors activated by the attended line was greater than that of neural responses of motion detectors activated by the unattended line. ( 4 ) One can conclude that, in the present study, the focusing of attention on one line of the stimulus caused the attended line to look longer because focused attention made the attended line expand perceptually more rapidly.

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