Eyal M. Reingold

Using direct and indirect measures to study perception without awareness.

Many studies directed at demonstrating perception without awareness have relied on the dissociation paradigm. Although the logic underlying this paradigm is relatively straightforward, definitive results have been elusive in the absence of any general consensus as to what constitutes an adequate measure of awareness. We propose an alternative approach that involves comparisons of the relative sensitivity of comparable direct and indirect indexes of perception. The only assumption required by the proposed approach is that the sensitivity of direct discriminations to relevant conscious information is greater than or equal to the sensitivity of comparable indirect discriminations. The proposed approach is illustrated through an evaluation of Avant and Thieman’s (1985) recent claim that an indirect measure of perception based on judgments of apparent visual duration provides a more sensitive indicator of perception than does a direct measure based on forced-choice recognition. Contrary to this claim, when direct and indirect indexes are measured under comparable conditions, an indirect measure based on judgments of perceived duration provides a less sensitive index of perceptual processing than do comparable direct measures. The proposed approach provides a general conceptual/methodological framework for using the dissociation paradigm in studies directed at establishing unconscious processes.

Visual Span in Expert Chess Players: Evidence From Eye Movements:

The reported research extends classic findings that after briefly viewing structured, but not random, chess positions, chess masters reproduce these positions much more accurately than less-skilled players. Using a combination of the gaze-contingent window paradigm and the change blindness flicker paradigm, we documented dramatically larger visual spans for experts while processing structured, but not random, chess positions. In addition, in a check-detection task, a minimized 3 × 3 chessboard containing a King and potentially checking pieces was displayed. In this task, experts made fewer fixations per trial than less-skilled players, and had a greater proportion of fixations between individual pieces, rather than on pieces. Our results provide strong evidence for a perceptual encoding advantage for experts attributable to chess experience, rather than to a general perceptual or memory superiority.

Toward a Redefinition of Implicit Memory: Process Dissociations Following Elaborative Processing and Self-Generation

Does conceptual processing affect unconscious uses of memory? We used a process-dissociation procedure to separate automatic (unconscious) and consciously controlled uses of memory in a stem-completion task. Contrary to results from indirect test conditions, estimates derived from our procedure showed no effect of self-generation and no differential effect of semantic and nonsemantic study conditions on automatic uses of memory. These results provide evidence that (a) indirect tests are often contaminated by conscious uses of memory and (b) stem completion is highly dependent on prior perceptual (and perhaps lexical) processing. The experiments demonstrate the advantages of using process-dissociation procedures over comparisons between direct and indirect tests.

The perceptual aspect of skilled performance in chess: Evidence from eye movements

Expert and intermediate chess players attempted to choose the best move in five chess positions while their eye movements were monitored. Experts were faster and more accurate than intermediates in choosing the best move. Experts made fewer fixations per trial and greater amplitude saccades than did intermediates, but there was no difference in fixation duration across skill groups. Examining the spatial distribution of the first five fixations for each position by skill group revealed that experts produced more fixations on empty squares than did intermediates. When fixating pieces, experts produced a greater proportion of fixations on relevant pieces than did intermediates. It is argued that expert chess players perceptually encode chess configurations, rather than individual pieces, and, consequently, parafoveal or peripheral processing guides their eye movements, producing a pattern of saccadic selectivity by piece saliency.

Saccadic Inhibition in Voluntary and Reflexive Saccades

The present study investigated saccadic inhibition in both voluntary and stimulus-elicited saccades. Two experiments examined saccadic inhibition caused by an irrelevant flash occurring subsequent to target onset. In each trial, participants were required to perform a single saccade following the presentation of a black target on a gray background, 4 to the left or to the right of screen center. In some trials (flash trials), after a variable delay, a 33-msec flash was displayed at the top and bottom third of the monitor (these regions turned white). In all experimental conditions, histograms of flash-to-saccade latencies documented a decrease in saccadic frequency, forming a dip, time-locked to the flash and occurring as early as 6070 msec following its onset. The fast latency of this effect strongly suggests a low-level, reflex-like, oculomotor effect, which was referred to as saccadic inhibition. A novel procedure was developed to allow comparisons of saccadic inhibition even across conditions, which in the absence of a flash (no-flash trials) produce dissimilar saccadic reaction times (SRTs) distributions. Experiment 1 examined the effects of the fixation stimulus on saccadic inhibition by contrasting three conditions: a gap condition (fixation stimulus disappeared 200 msec prior to target onset), a step condition (offset of the fixation stimulus was simultaneous with target onset), and an overlap condition (the fixation stimulus remained on for the duration of the trial). The overlap condition produced substantially stronger saccadic inhibition, relative to the gap and the step conditions. Experiment 2 contrasted the saccadic inhibition effect obtained for prosaccades (saccades aimed at the target) with the effect obtained for antisaccades (i.e., saccades aimed away from the same target). The onset of saccadic inhibition was earlier, and its magnitude was stronger, for antisaccades, relative to prosaccades. The plausibility that the superior colliculus is the neurophysiological locus of the saccadic inhibition effect was explored.

Recognition and lexical decision without detection : unconscious perception?

Stimulus detection and concurrent measures of stimulus recognition were compared to establish whether perception occurs in the absence of detection. The target stimuli were familiar words (Experiments 1 and 2), nonwords (Experiment 3), or both words and nonwords (Experiment 4). On each trial, either a stimulus or a blank field was presented. Ss first decided whether a stimulus had been presented and then made either a forced-choice recognition decision (Experiments 1, 2, and 3) or a lexical decision (Experiment 4). Both words and nonwords were recognized and discriminated following correct detections (i.e., hits). However, in the absence of stimulus detection (i.e., misses), only words were recognized or discriminated. These qualitatively different patterns of results following hits and misses for words and nonwords suggest that stimulus detection may provide an adequate measure of conscious awareness.

Gaze-contingent multiresolutional displays: an integrative review.

Gaze-contingent multiresolutional displays (GCMRDs) center high-resolution information on the users gaze position, matching the users area of interest (AOI). Image resolution and details outside the AOI are reduced, lowering the requirements for processing resources and transmission bandwidth in demanding display and imaging applications. This review provides a general framework within which GCMRD research can be integrated, evaluated, and guided. GCMRDs (or “moving windows”) are analyzed in terms of (a) the nature of their images (i.e., “multiresolution,” “variable resolution,” “space variant,” or “level of detail”), and (b) the movement of the AOI (i.e., “gaze contingent,” “foveated,” or “eye slaved”). We also synthesize the known human factors research on GCMRDs and point out important questions for future research and development. Actual or potential applications of this research include flight, medical, and driving simulators; virtual reality; remote piloting and teleoperation; infrared and indirect vision; image transmission and retrieval; telemedicine; video teleconferencing; and artificial vision systems.

Distractor Ratio Influences Patterns of Eye Movements during Visual Search

We examined the flexibility of guidance in a conjunctive search task by manipulating the ratios between different types of distractors. Participants were asked to decide whether a target was present or absent among distractors sharing either colour or shape. Results indicated a strong effect of distractor ratio on search performance. Shorter latency to move, faster manual response, and fewer fixations per trial were observed at extreme distractor ratios. The distribution of saccadic endpoints also varied flexibly as a function of distractor ratio. When there were very few same-colour distractors, the saccadic selectivity was biased towards the colour dimension. In contrast, when most of the distractors shared colour with the target, the saccadic selectivity was biased towards the shape dimension. Results are discussed within the framework of the guided search model.

Visual search asymmetry: The influence of stimulus familiarity and low-level features

Wang, Cavanagh, and Green (1994) demonstrated a pop-out effect in searching for an unfamiliar target among familiar distractors (U—F search) and argued for the importance of a familiarity difference between the target and the distractors in determining search efficiency. In four experiments, we explored the generality of that finding. Experiment 1 compared search efficiency across a variety of target-distractor pairs. In Experiments 2, 3, and 4, we used Chinese characters and their transforms as targets and distractors and compared search performance between Chinese and non-Chinese participants. We demonstrated that search asymmetry and search efficiency in the U—F condition are influenced by the presence of low-level feature differences between the familiar and the unfamiliar stimuli. Our findings suggest that the familiarity of the distractors, rather than the familiarity difference between the target and the distractors, determines search efficiency. We also documented a counterintuitive familiarity-inferiority effect, suggesting that knowledge of search stimuli may, sometimes, be detrimental to search performance.

Preattentive guidance of eye movements during triple conjunction search tasks: the effects of feature discriminability and saccadic amplitude.

Eye movements were monitored during the performance of triple conjunction search tasks. Stimuli varied in color, shape, and orientation. Across trials, the target was either present or absent, and displays consisted of 6, 12, or 24 stimuli. Stimulus discriminability was manipulated for the shape dimension, with half of the participants seeing displays of Es and Fs (low-discriminability [LD] condition) and half seeing displays of Cs and Ts (high-discriminability [HD] condition). Participants in both conditions performed two search tasks. In the single-feature (SF) task, the target stimulus shared one feature with each of the distractors, whereas in the two-feature (TF) task, it shared two features with each distractor. An examination of saccadic endpoints revealed that participants were more likely to fixate on distractor stimuli sharing color (SF task) or color and shape (TF task) with the target. This was a robust finding, being observed across participants, saccades of different amplitudes and sequential position, and following short and long latencies to move. The extent to which participants made use of shape information increased with discriminability.