Measuring the 'Tunnel Effect' with Change Detection
 
 
Here are some demonstrations of the various conditions discussed in the following paper:
Flombaum, J. I., & Scholl, B. J. (2006). A temporal same-object advantage in the tunnel effect: Facilitated change detection for persisting objects. Journal of Experimental Psychology: Human Perception & Performance, 32(4), 840-853.
These demonstrations are provided as Quicktime movies, which can be downloaded or viewed directly in most web-browsers. (To download a free Quicktime player, go here.) These movies are a bit large and choppy, but they should be sufficient to illustrate the basic conditions. As highly compressed versions of the original stimuli, these movies may not preserve the precise spatial and temporal characteristics of the originals.  
 
This project explores the ways in which the visual system identifies objects as the same enduring individuals through time, motion, and periods of occlusion -- and despite featural change. Here we explore object persistence in an especially direct way using a new variant of the tunnel effect: When an object moves behind an occluder (the 'tunnel') and then an object later emerges, we often irresistibly perceive the continuous motion of a single persisting object. This percept occurs even when the pre- and post-occlusion views are featurally distinct, so long as the perceived trajectory is spatiotemporally consistent. In this project we introduce a new change-detection method of measuring and quantifying percepts of the tunnel effect: observers viewed displays in which several objects oscillated behind occluders. Objects occasionally changed color while occluded, and observers simply had to detect these changes (pressing a key each time they observed a change).  
 
Sample Animation from Experiment 1 (1.4 MB)  
Experiment 1 involved three conditions: (1) Tunnel Events, with spatiotemporally continuous motion, resulting in the percept of a single object which momentarily occludes and disoccludes; (2) Temporal Gap Events, wherein the objects always disoccluded at the right place but the wrong time (after a brief pause, during each pass behind the occluder); and (3) Spatial Gap Events, wherein the objects disoccluded at the right time but the wrong place (in different vertical locations than the ones at which they originally became occluded). Both types of gaps eliminated the percept of object persistence, such that each 'gap' event could be seen as involving two distinct objects. On each trial, subjects watched a 15-second animation such as the one provided here. This movie depicts a trial with one event of each type. Subjects detected a greater proportion of color changes in Tunnel events than in the other events. This reveals a new type of temporal 'same-object advantage': change detection is improved across temporal scene fragments that are bound into the same persisting object representations. This demonstrates the importance of object persistence for visual memory, and illustrates how the tunnel effect can be studied in an implicit manner.  
 
Sample Animation from Experiment 2 (1.9 MB)  
Experiment 2 involved events of the same three types, but now the occluders moved while the objects remained stationary. In this experiment, observers detected an equal proportion of changes in the Tunnel and Temporal Gap events, since the Temporal Gaps with moving occluders still yielded the percept of a single object. This demonstrates that the results of Experiment 1 were due to object persistence, and not to brute psychophysical properties such as the delay before an object disoccluded (which was controlled here).  
 
Sample Animation from Experiment 3 (Implosion/Explosion Block) (284 KB)
Sample Animation from Experiment 3 (Occlusion/Disocclusion Block) (300 KB)  
Experiment 3 employed a new cue to object persistence: when objects 'implode' and 'explode' at occluder boundaries, change detection is impaired relative to standard occlusion and disocclusion -- despite the fact that the objects disappear at the same times, locations, and rates in each case. When objects 'implode', the visual system infers that they have gone out of existence (rather than out of sight); this causes the visual system to discard that object representation, which impairs the detection of changes made between it and a subsequent view. (Note that the trials in this experiment also included stationary disctractors, and that the 'target' objects flash at the beginning of the trial before they begin moving.)