Change Blindness

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Visual attention reveals changing color in moving objects James E. Hoffman and Scott McLean University of Delaware

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Visual attention reveals changing color in moving objects James E. Hoffman and Scott McLean University of Delaware. Change Blindness. Alternating pictures differing in one feature or object Usually accompanied by a mask or irrelevant transient, that results in “change blindness”. - PowerPoint PPT Presentation

Transcript of Change Blindness

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Visual attention reveals changing color in moving objects

James E. Hoffman and Scott McLeanUniversity of Delaware

Change BlindnessAlternating pictures differing in one feature or object

Usually accompanied by a mask or irrelevant transient, that results in change blindness

The transient elicited by the onset of the mud splashes swamps the transient accompanying the onset of the gap in lane marker. Attending to the location of the change, restores its visibility.

The difficulty of detecting changes reflects a limited capacity system. We cant attend to all of the locations in the picture at the same time.

3Seeing the Transient

Attention and Change DetectionThe transient in the second presentation automatically captures attention, leading to awareness of the changing feature.

The mudsplashes in the first presentation provide additional transients that mask those produced by the changing lane marker. If attention is directed to the location of the change, awareness of the change is restored.

Note that this experiment also reveals the limited-capacity nature of visual attention. Apparently we can only attend to a few objects in the picture at any given time. Motion-induced change blindnessSuchow and Alvarez (2011) recently introduced a striking form of change blindness that may require a different mechanism to explain a failure of awareness for change.

In their illusion, all the objects are changing instead of just one and the illusion persists even though the observer attends to the objects and knows that they are changing (abstract)

They called this effect motion silencing

Motion Silencing of Color Change

The same effect occurs for changes in shape, lightness, and sizeRecently, Suchow and Alvarez (2011) introduced a striking form of change blindness that won the Vision Societys Best illusion of the year aware in 2011.

They showed that simply setting objects into motion can block awareness of changes that would be impossible to miss when the objects are stationary. They called this motion silencing.

8What Causes Motion Silencing?David Burr, in a commentary accompanying the original article, suggested that two factors are responsible for Motion Silencing:

Motion coherenceWhen a crowd of objects moves coherently together, perceiving the individual objects may be difficult (Poljac et al., 2012). Similar to global precedence effect.CrowdingClose objects may not be individuated. In this case, the observer may not be able to assign successive colors to a single object. In contrast, stationary dots will still stimulate retinotopic change detectors that can signal the presence of a change (Turi and Burr, 2013).

The role of attention in motion silencingWe suggest that in motion silencing, the color change is masked by transients associated with motion and that locating the color change requires attention, just like the mud splash experiment. Coherent motion and crowding are not the causes of the motion silencing effect; they simply modulate its strength through their effect on the real causal mechanism which is visual attention.

Coherent motion and crowding both increase the difficulty of paying attention to individual objects but the illusion should still occur when motion coherence and crowding are eliminated, as long as the display exceeds the observers ability to attend to all of the objects in parallel. Current StudyIn the current study, we evaluated the effects of attention by asking observers to track 1, 2, or 3 target objects embedded in a display of distractors (MOT). Detection of color change should be much better for changes occurring on targets compared to distractors and should be closely related to tracking accuracy .

In contrast, performance with static displays should be high and independent of set size.

We also attempted to determine whether silencing can be obtained with incoherent motion and uncrowded displays which would show that these variables are not crucial ingredients of the motion silencing effect. 11Trial EventsMovingStationary

Static DisplayCue Display Set Size =3Motion (2 sec.)No Color ChangeColor Change occurs on a Target or a Distractor

Tracking TrialsColor Change TrialsClick on Target Dots12Results

Observers missed approximately 1% of the changes with static displays while they missed 36% of the changes with moving displays.

This is essentially a replication of the motion silencing effect for our paradigm.Attend all conditionReplication of the motion silencing effectResults: Tracking Accuracy

Observers were limited in their ability to accurately track more than a few objectsChange Detection

Attend AllStatic ControlChange Detection was at ceiling in the stationary condition and was unaffected by set size or attention

Change Detection was mediated by retinotopic change detectorsset sizePercent CorrectDoes change detection on distractors depend on their distance from a target?

Close: 1.42deg to 1.61 dvaMedium: 1.63 to 2.02 dvaFar: > 2.03 dvaNo ..But it does depend on distance from fixation

SummaryLike previous studies on change blindness, detection of change in motion silencing was heavily dependent on whether or not the change was attended.

In the next experiment, we show that motion silencing still occurs when displays are uncrowded and still depends on attention being allocated to the changing object

Expt. 2: Silencing with Uncrowded Displays+Sparse Displays containing only 10 objects

Observers tracked two objects or attended to all of them

Objects appeared as either stationary or movingSilencing with Uncrowded Displays+Minimum inter-object spacing was large enough to eliminate crowding for the most peripheral objects, i.e., there is no crowding in these displays. Do we still get motion silencing?ResultsTracking accuracy

Moving: 94.7%Stationary: 98.1%

Corresponding Data from Expt. 1.

UncrowdedConclusionsNeither crowding nor motion coherence are necessary conditions for motion silencingMotion silencing may be due to masking of change signals by object motionAttention to individual moving objects isolates them from these masking signals allowing the change signal to emergeEffects of crowding and coherence may be seen as factors that modulate the difficulty of attending to individual objectsColor change detection appears be a useful tool for studying the role of visual attention in MOT

Thanks!

Does attention affect motion silencing?Suchow and Alvarez suggested that it might:Conceivably, the brief exposure afforded by a fast-movingobject could be lengthened by rapidly shifting the focus ofattention over a moving window [10, 11]. Here, tight spacingprecluded isolation, and explicit instructions to pay attentionto the whole set discouraged any shifts of attention. Manipulatingthe number of dots or asking observers to attend toonly a few of them might reveal the role of attention insilencing. (p. 141)

But Turi and Burr suggest that motion silencing seems to resistattention to individual dots. (p.1)