Joseph Tzelgov

SUPPRESSION SITUATIONS IN PSYCHOLOGICAL RESEARCH : DEFINITIONS, IMPLICATIONS, AND APPLICATIONS

In 1941, Horst noticed that a variable can be totally uncorrelated with the criterion and still improve prediction by virtue of being correlated with other predictors. He christened such variables suppressors, a title that implies that such variables suppress criterion-irrelevant variance in other predictors. During the 50 years that have passed since Horsts original analysis, the concept of suppression has been extended and reanalyzed. What follows provides a general approach to the analysis of suppression situations. This approach is based on coupling the analysis of 3 variate suppression situations with the applications of the concept of suppressor to the general linear model. The implications of the analysis are discussed, and some applications of the concept of suppression are provided.

Is three greater than five: the relation between physical and semantic size in comparison tasks.

In this study, subjects were asked to judge which of two digits (e.g., 3 5) was larger either in physical or in numerical size. Reaction times were facilitated when the irrelevant dimension was congruent with the relevant dimension and were inhibited when the two were incongruent (size congruity effect). Although judgments based on physical size were faster, their speed was affected by the numerical distance between the members of the digit pair, indicating that numerical distance is automatically computed even when it is irrelevant to the comparative judgment being required by the task. This finding argues for parallel processing of physical and semantic information in this task.

Controlling Stroop effects by manipulating expectations for color words.

An important characteristic of automatic processing is its uncontrollability, The Stroop phenomenon is regarded as a prototypical example of this characteristic of automatic processing, hence, the Stroop effect should not change when the percentages of color words versus neutral stimuli are manipulated to induce controlled processing. We found that Stroop interference decreased as the percentage of color words increased. Furthermore, the magnitude of the inhibitory component of the Stroop effect was negatively correlated with the percentage of color words; the facilitatory component was insensitive to the manipulation. These results suggest that the Stroop effect is controllable (see Logan, 1980) and that the locus of control is postlexical. The results also suggest that facilitation and inhibition are produced by different mechanisms and challenge those models of the Stroop phenomenon (e.g., Cohen, Dunbar, & McClelland, 1990; Phaf, Van der Heijden, & Hudson, 1990) that assume that a single processing mechanism causes facilitation and inhibition and that control affects facilitation and inhibition alike (Logan, 1980).

Distinguishing between Automaticity and Attention in the Processing of Emotionally-Significant Stimuli.

There is contradicting evidence as to whether irrelevant but significant emotional stimuli can be processed outside the focus of attention. In the current study, participants were asked to ignore emotional and neutral pictures while performing a competing task. In Experiment 1, orienting of attention to distracting pictures was manipulated via a peripheral cue. In Experiment 2, attentional load was varied, either leaving spare attention to process the distracting pictures or, alternatively, depleting attentional resources. Although all pictures were task irrelevant, negative pictures were found to interfere more with performance in comparison to neutral pictures. This finding suggests that processing of negative stimuli is automatic in the sense that it does not require execution of conscious monitoring. However, interference occurred only when sufficient attention was available for picture processing. Hence, processing of negative pictures was dependent on sufficient attentional resources. This suggests that processing of emotionally significant stimuli is automatic yet requires attention.

Automatic processes in lexical access and spreading activation.

The semantic priming effect can be reduced or eliminated depending on how the prime word is processed. The experiments reported here investigate this prime task effect. Two experiments used identity and semantic priming tasks to determine whether the prime word is encoded at a lexical level under letter-search conditions. When the prime task was naming, both identity and semantic priming occurred; however, when a letter-search task was performed on the prime word, only identity priming occurred, thus supporting the argument that the search task affects activation of semantic associates rather than lexical access of the prime word. Another experiment demonstrated that this identity priming was the result of lexical processes rather than of letter-by-letter priming. A cross-modal priming technique demonstrated that the letter-search prime task does not actively suppress activation of semantic associates. The implications of these results for automaticity and for proposed mechanisms of priming are discussed.

Capacity demands of automatic processes in semantic priming

Ben-Gurion University of the Negev, Beer Sheva, Israel In three experiments, we examined the effects of prime-target stimulus onset asynchrony (SOA) and the proportion of related primes and targets (relatedness proportion, or RP) on semantic priming when the prime was either named or was searched for a specific letter. In Experiment 1, with an RP of. 50, priming occurred at SOAs of 240 and 840 msec when the prime was named, but no priming was found at either SOA when the prime was searched for a letter. In Experiment 2 the RP was either. 20 or. 80, and the SOA was set at 1, 700 msec; priming again was found in both conditions when the prime was named, but only in the RP.80 condition when a letter search task was performed on the prime. In Experiment 3, both the proportion of related trials and SOA were varied; as in the previous experiments, no priming effects were found with the letter search task for either SOA in the RP.20 condition, but the priming effect was reinstated in the RP.80 condition. These results are discussed with respect to how limited capacity resources are allocated and how they influence semantic priming effects.

Automaticity of two-digit numbers.

Automatic processing of 2-digit numbers was demonstrated using the size congruency effect (SiCE). The SiCE indicates the processing of the irrelevant (numerical) dimension when 2 digits differing both numerically and physically are compared on the relevant (physical) dimension. The SiCE was affected by the compatibility between unit and decade digits but was unaffected by the global magnitude of the numbers. Together these results suggest automatic processing of the magnitudes of the components of the 2-digit numbers but not of whole numbers. Finally, the SiCE was affected more by the magnitude of the decade digits compared with the unit digits, indicating that the syntactic roles of the digits were represented. The implications of these results for understanding the numerical representations are discussed.

Automatic comparisons of artificial digits never compared: learning linear ordering relations.

In 2 experiments, participants were trained to perform magnitude decisions, that is, decide which of 2 arbitrary symbols in a pair represented a larger magnitude. The symbols corresponded to locations on an implicit linear scale. Training resulted in a Stroop-like size congruity effect when the participants had to decide which symbol in a pair was physically larger. This effect, showing automaticity of the processing of magnitude relations, was also obtained for pairs never encountered during practice. The implications of these findings for processing of magnitude relations and for theories of automaticity are discussed.

UNINTENTIONAL WORD READING VIA THE PHONOLOGICAL ROUTE : THE STROOP EFFECT WITH CROSS-SCRIPT HOMOPHONES

Single-route theories that argue that access to meaning is always mediated by phonology are consistent with process theories of automaticity. Dual-route theories, suggesting that reading skill results in direct access, are consistent with the notion of automaticity as memory retrieval. If word reading reflects memory retrieval, the Stroop effect should be absent in the absence of cues normally serving for retrieval. The Stroop effect was obtained in Hebrew-English bilinguals for cross-script homophones, which have meaning as color names in one language but are written in a script of the other language. The Stroop effect in cross-script homophones was independent of response mode and was insensitive to color-related proportion, supporting the assumption of different routes being involved in access to meaning of regular words and cross-script homophones. Implications for automaticity, theories of word reading, and knowledge representation by bilinguals are discussed. Reading is a cognitive skill that most humans acquire early and use extensively during their lives. The term word reading, as used by us, refers to mapping from strings of graphemes (i.e., written words) to meaning, when such strings are presented in isolation. Because extensive practice leads to automatic processing (Logan, 1988a), most investigators agree that word reading, at least in skilled readers, is an automatic process. In this article we analyze word reading from the viewpoint of approaches to automaticity. Our study has implications for theories of automaticity on the one hand and for theories of word reading on the other. In addition, because of the special kinds of stimuli we used, our findings are also relevant to the issue of knowledge representation by bilinguals.

On stereo image coding

An approach to stereo image compression based on disparity compensation is proposed and evaluated. The scheme is motivated by the suppression theory in human vision. A methodology for evaluating compressed stereo images is proposed. It is based on time measurements of depth perception tasks performed by human subjects. Subjects taking part in the experiment were exposed to displays of stereo images, some of which had been compressed, and were asked to judge the relative depth within each display as fast as possible. Decision times were measured and used as the major dependent variable. It was found that very deep compression of one of the images of a stereo pair does not interfere with the perception of depth in the stereo image.<<ETX>>