Nurit Gronau

Behavioral and physiological measures in the detection of concealed information.

The authors examined the incremental validity of the reaction time (RT) measure beyond that of skin conductance response (SCR) in the detection of concealed information. Participants performed a Stroop-like task in which they named the color of critical and neutral words. Results show that the SCR highly differentiated between the relevant and neutral words. However, the RT demonstrated a significant differentiation only when the critical words denoted personally significant items (e.g., ones own name) and not when they denoted crime-relevant items related to a simulated crime. In both cases, combining the 2 measures yielded no advantage over the use of SCR alone. Thus, although behavioral measures may differentiate between relevant and neutral information in some cases, their practical use is questionable.

Associative recognition processes are modulated by the semantic unitizability of memoranda

Although memory of episodic associations is generally considered to be recollective in nature, it has been suggested that when stimuli are experienced as a unit, familiarity processes might contribute to their subsequent associative recognition. To investigate the effect of semantic relatedness during episodic encoding on the processes of retrieval of associative information, we had participants interactively encode pairs of object pictures, vertically arranged so as to suggest a functional or configural relationship between them. Half the pairs were independently judged to be of related objects (e.g., a lamp over a table) and half of unrelated objects (e.g., a key-ring over an apple). At test, participants discriminated between intact, recombined, and new pairs while event related potentials (ERPs) were recorded. In an early ERP marker of retrieval success generally associated with familiarity processes, differences related to associative memory only emerged for related pairs, while differences associated with item memory emerged for both related and unrelated pairs. In contrast, in a later ERP effect associated with recollection, differences related to associative memory emerged for both related and unrelated pairs. These findings may indicate that retrieval of episodic associations formed between two semantically related visual stimuli can be supported by familiarity-related processes.

Prelexical phonologic computation in a deep orthography: Evidence from backward masking in Hebrew

Prelexical phonological computation of print was examined in Hebrew orthography using backward masking. Target words were masked by homophonic, phonologically similar, or phonologically dissimilar nonwords. Phonological similarity between masks and targets affected detection in a nonlinear fashion: No differences were found between homophonic and phonologically similar masks, whereas phonologically dissimilar masks hindered identification dramatically. This suggests that representations computed in brief exposures are coarse grained and not detailed enough to capture fine phonetic differences.

Contextual integration of visual objects necessitates attention.

Objects that form a contextually coherent percept are grasped more rapidly and efficiently than objects that are contextually inconsistent with each other. The extent to which such clustering processes depend on visual attention is largely unknown. The present research examined the necessity of attention for object-to-object contextual integration processes during a brief visual glimpse. Participants performed an object classification task on associated object pairs that were presented for a short duration (59 ms). Objects were positioned either in expected relative locations (e.g., a desk lamp on a desk) or in unexpected relative locations (e.g., a desk lamp under a desk). When both stimuli were relevant to task requirements, latencies to spatially consistent object pairs were significantly shorter than those to spatially inconsistent pairs (Experiment 1). These contextual effects disappeared, however, when spatial attention was drawn to one of the two object stimuli while its counterpart object appeared outside the main focus of attention, serving as a task-irrelevant distractor (Experiment 2). Attentional modulation of contextual integration processes was shown to be independent of distractor recognition per se (Experiment 3). Finally, the role of goal-directed (endogenous) and spatial (exogenous) attention factors in contextual integration was explored (Experiment 4). Taken together, our findings suggest that contextual associations play an important role in processing multiple-object visual displays. However, regardless of whether objects are associated by active or passive relations, the construction of a coherent contextual representation strongly relies on the availability of attentional capacity. Possible implications for theories of scene and object recognition are discussed.

Distractor interference in focused attention tasks is not mediated by attention capture

Distractor stimuli possessing information that is relevant for a task (henceforth, task-relevant distractors) often interfere with task performance. The interference by task-relevant distractors is observed even when distractors are positioned outside the main attentional focus. We investigated whether such interference is due to an attention capture by the distractors. Participants responded to a target colour while ignoring word distractors positioned within (Experiment 1) or outside (Experiments 2 and 3) the attentional focus. The words carried task-relevant information in their colour and personally significant information in their content. Because personally significant information affects performance only when positioned in an attended region, it was used as a marker for the locus of the attentional focus. As expected, when distractors were attended, both task-relevant and personally significant information affected performance. However, when distractors were unattended, only task-relevant information caused interference, suggesting that attention did not shift to the distractors’ location. We discuss possible accounts for interference effects in focused-attention tasks.

The effect of novel distractors on performance in focused attention tasks: A cognitive-psychophysiological approach

In the present study, we examined whether or not novel stimuli affect performance in a focused attention task. Participants responded to a central target while an irrelevant distractor in the visual display was occasionally changed. In Experiment 1, both target and distractor were presented centrally within the focus of attention. In Experiment 2, a central target was presented along with an irrelevant distractor at a peripheral location, outside the focus of attention. Novel distractors were associated with longer latencies and enhanced orienting responses (as measured by skin conductance responses) only when presented at an attended location. In contrast, as is demonstrated in Experiment 3, the same peripheral novel distractors interfered with task performance when they possessed task-relevant information. These results indicate that there is a fundamental difference between novel stimuli and task-relevant stimuli. Whereas the former exert influence only within the focus of attention, the latter affect performance even when positioned in an unattended location. Our findings have important implications for the operation of visual attention.

Algorithms for detecting concealed knowledge among groups when the critical information is unavailable.

We examined whether the Concealed Information Test (CIT) may be used when the critical details are unavailable to investigators (the Searching CIT [SCIT]). This use may have important applications in criminal investigations (e.g., finding the location of a murder weapon) and in security-related threats (e.g., detecting individuals and groups suspected in planning a terror attack). Two classes of algorithms designed to detect the critical items and classify individuals in the SCIT were examined. The 1st class was based on averaging responses across subjects to identify critical items and on averaging responses across the identified critical items to identify knowledgeable subjects. The 2nd class used clustering methods based on the correlations between the response profiles of all subject pairs. We applied a principal component analysis to decompose the correlation matrix into its principal components and defined the detection score as the coefficient of each subject on the component that explained the largest portion of the variance. Reanalysis of 3 data sets from previous CIT studies demonstrated that in most cases the efficiency of differentiation between knowledgeable and unknowledgeable subjects in the SCIT (indexed by the area under the receiver operating characteristic curve) approached that of the standard CIT for both algorithms. We also examined the robustness of our results to variations in the number of knowledgeable and unknowledgeable subjects in the sample. This analysis demonstrated that the performance of our algorithms is relatively robust to changes in the number of individuals examined in each group, provided that at least 2 (but desirably 5 or more) knowledgeable examinees are included.

The necessity of visual attention to scene categorization: Dissociating “task-relevant” and “task-irrelevant” scene distractors.

The extent to which scenes are categorized and understood in the absence of attention has been the focus of a continuous debate over the last decade. Most studies investigating this question have used experimental paradigms in which participants explicitly searched for a certain scene category, or alternatively, scenes were task-irrelevant yet their identity was explicitly reported by participants. Although the first type of studies may have overestimated unattended scene processing, the latter type of studies may have underestimated scene processing due to the reliance on subjective response criteria and on working memory capacity limits. The present research examined scene processing by using an implicit, online behavioral measure which assessed the influence of both task-relevant (i.e., to-be-detected) and task-irrelevant distractor scenes on behavior. The effect of scene categorization was compared when scenes were fully attended (Experiment 1) versus when they were positioned in an unattended location and served as relevant/irrelevant distractors (Experiments 2 and 3). Our results demonstrated that in contrast to attended scenes, unattended distractor scenes which were not part of one’s task-set were not automatically categorized and did not exert influence on performance. Critically, however, the very same scene distractors affected behavior when they contained a to-be-detected category, suggesting a qualitative dissociation between task-relevant and task-irrelevant distractors. Our study provides a systematic examination of scene distractor processing outside the focus of visual attention and a framework that may reconcile previous conflicting evidence.

Age effects on associative memory for novel picture pairings

Normal aging is usually accompanied by greater memory decline for associations than for single items. Though associative memory is generally supported by recollection, it has been suggested that familiarity can also contribute to associative memory when stimuli can be unitized and encoded as a single entity. Given that familiarity remains intact during healthy aging, this may be one route to reducing age-related associative deficits. The current study investigated age-related differences in associative memory under conditions that were expected to differentially promote unitization, in this case by manipulating the spatial arrangement of two semantically unrelated objects positioned relative to each other in either spatially implausible or plausible orientations. Event-related potential (ERP) correlates of item and associative memory were recorded whilst younger and older adults were required to discriminate between old, recombined and new pairs of objects. These ERP correlates of item and associative memory did not vary with plausibility, whereas behavioral measures revealed that both associative and item memory were greater for spatially plausible than implausible pair arrangements. Contrary to predictions, older adults were less able to take advantage of this memory benefit than younger participants. Potential reasons for this are considered, and these are informed by those lines of evidence which indicate older participants were less sensitive to the bottom-up spatial manipulation employed here. It is recommended that future strategies for redressing age-related associative deficits should take account of the aging brains increasing reliance on pre-existing semantic associations.

Counting distance: Effects of egocentric distance on numerical perception

Numerical value is long known to be associated with a variety of magnitude representations, such as size, time and space. The present study focused on the interactive relations of numerical magnitude with a spatial factor which is dominant in everyday vision and is often overlooked, namely, egocentric distance, or depth. We hypothesized that digits denoting large magnitudes are associated with large perceived distances, and vice versa. While the relations of numerical value and size have been long documented, effects of egocentric distance on numeral perception have been scarcely investigated, presumably due to the difficulty to disentangle size and depth factors within three-dimensional visual displays. The current study aimed to assess the potential linkage between egocentric distance and number magnitude, while neutralizing any perceived and/or physical size parameters of target digits. In Experiment 1, participants conducted a numeral size-classification task (‘bigger or smaller than 5’), to which they responded with a near-to-body or a far-from-body key. Results revealed shorter responses for small than for large numbers when responded with a key positioned close to the body, and for large than small numbers when responded with a key positioned far from the body (regardless of hand-key mapping). Experiment 2 used verbal stimuli denoting near/remote concepts as irrelevant primes to target digits, further demonstrating a priming effect of conceived distance on numerical value processing. Collectively, our results suggest that distance magnitudes are associatively linked to numerical magnitudes and may affect digit processing independently of the effects of visual size.