Sequential modulations of interference evoked by processing task-irrelevant stimulus features

Compatibility level repetition benefits in interference paradigms have been taken to reflect enhanced processing selectivity in response to cognitive conflict elicited by a task-irrelevant stimulus feature. The authors demonstrate such sequential effects in the Simon task which (a) occur independent of previous behavioral conflict effects and (b) cannot be accounted for by selectivity enhancement. Furthermore, when presenting more than one type of irrelevant stimulus features, compatibility level repetition effects occurred in a type-specific manner. The results do not support the notion that cognitive conflict results in enhanced processing selectivity and favor a feature integration account.     

The effects of grouping visual stimuli on the cortical evoked potential

The University Of Michigan. Ann Arbor. Michigan The effect of grouping elements of a visual stimulus on the amplitude of the bipolar occipital evoked potential is considered in two experiments. A marked and orderly relation is found. Various classes of hypotheses are advanced to account for this finding.     

Sequential resolution of fragmented visual percepts: experimental investigation of a subject's perceptual experience after a right medial temporal stroke

This report concerns the fragmented visual percepts in a woman, TR, following a right entorhinal-perirhinal infarct. In a previous report, Weddell [Weddell, R. A. (2005). A visual disorder producing highly selective deletion of recurring letters. Cortex, 41, 471-485] linked TR's highly selective tendency to delete recurrent letters with her fragmented percepts. The conflation of same-identity form elements was attributed to anterior extrastriate damage, which reduced the amount of information sustainable in fully resolved visual percepts, and the present experimental investigation of her subjective account of segment formation and resolution completes the story. She said that complex objects and long words first appeared as blurred regions, which sometimes included form elements. It is argued that figure-centred attentional mechanisms subdivided this blurred region into up to 3-4 parts. String length, lexical status (word vs. nonword), and background colour and/or luminance determined fragment length. Two rules described the fragment resolution sequence: largest segments usually resolved first, left-to-right resolution accounting for a few sequences. This resolution sequence occurred when stimuli were exposed too briefly for saccadic exploration, implicating endogenous attentional shifts. Experiment 4 confirmed TR's assertion that spatial, orthographic, and phonological information were stored during the fragment resolution process. Moreover, TR exerted considerable voluntarily control over the fragment resolution sequence and some influence over fragment length. Finally, these findings were interpreted in terms of an extended version of a neural network model of vision largely derived from nonhuman primate studies.     

The time course of perceptual grouping: the role of segregation and shape formation

The time course of perceptual grouping was examined in two experiments, using a primed matching task. In different conditions, elements were grouped into columns/rows by common lightness, into a shape (triangle/ arrow or square/cross) by common lightness, and into a shape without segregation of elements. The results showed an early and rapid grouping into columns/rows by common lightness and into a shape when no segregation from other elements was involved. Goodness of shape (i.e., triangle/arrow vs. square/cross) had no influence on how early grouping was evident, but the relatively poorer shapes appeared to consolidate with time. In contrast, grouping into a shape that involved segregation and required resolving figure-ground relations between segregated units, as grouping into a shape by common lightness, consumed time, regardless of shape goodness. These results suggest that the time course of grouping varies as a function of the processes involved in it (e.g., segregation and shape formation) and the conditions prevailing for each process.     

On loudness enhancement of a tone burst by a preceding tone burst

The loudness level of a second tone burst in a monotic burst pair is investigated as a function of the intensity and frequency of the first burst relative to the corresponding variables of the second burst and as a function of the interburst time interval. The loudness level is measured with the help of a third, comparison burst whose frequency is the same as that of the second burst. The results, in connection with preceding results, show beyond any reasonable doubt that loudness effects in pairs of sound bursts are controlled by two perceptual processes: loudness enhancement and loudness summation. The first refers to the loudness of the second burst, the second, to the overall loudness of the burst pair. The time and frequency functions of the two processes are fundamentally different.     

Some further studies on the effect of grouping elements of a visual stimulus on the cortical evoked potential

Grouping elements of a visual stimulus is shown to reduce the amplitude of the bipolar occipital evoked potential in three experiments. The first shows similar effects of grouping elements on the horizontal and vertical dimensions, combining in a nearly additive manner. The second shows a less stable grouping effect using irregularly spaced lines as stimuli. In the third experiment, small deviations from uniformity are seen to produce a reliable attenuation of the cortical evoked potential.     

Aftereffect arising from unidirectional change of sound level in a tone: frequency specificity with a complex adaptor

Subjects adapted to square-wave adaptors, stimuli containing odd harmonics of the fundamental, and, to provide baseline data, sinusoidal adaptors matching the square-wave's fundamental. Nulls were obtained for various frequencies of the test stimulus. At any given frequency, the baseline null was subtracted from the null for square-wave adaptation. These corrected nulls indicated frequency-specific aftereffects at the third and fifth harmonics. The evidence is consistent with previous attempts to link the aftereffect of changing sound level in a tone with the auditory movement aftereffect because the latter may also show frequency specificity.     

Detectability of the deletion of a tone from a tone-plus-noise background

The deletion of a 1,000-Hz tone from a tone-plus-noise background is much harder for humans to detect than the insertion of the same tone into a background of noise. A mathematically ideal O, oblivious to the context in which an observation interval occurs, performs equally well under conditions of insertion and deletion. Human listeners, not oblivious to context, produced the function d_s = 0.036 E/N_o under deletion; the slope of this linear function is no more than half that of the typical slope of the comparable insertion function. The underlying reasons for the superiority of detection of insertion to that of deletion remain unclear.     

Reexamining the possible benefits of visual crowding: dissociating crowding from ensemble percepts

Peripheral objects and their features become indistinct when closely surrounding but nonoverlapping objects are present. Most models suggest that this phenomenon, called crowding, reflects limitations of visual processing, but an intriguing idea is that it may be, in part, adaptive. Specifically, the mechanism generating crowding may simultaneously facilitate ensemble representations of features, leaving meaningful information about clusters of objects. In two experiments, we tested whether visual crowding and the perception of ensemble features share a common mechanism. Observers judged the orientation of a crowded bar, or the ensemble orientation of all bars in the upper and lower visual fields. While crowding was predictably stronger in the upper relative to the lower visual field, the ensemble percept did not vary between the visual fields. Featural averaging within the crowded region does not always scale with the resolution limit defined by crowding, suggesting that dissociable processes contribute to visual crowding and ensemble percepts.     

Evaluating a computational model of perceptual grouping by proximity

A formal approach to the phenomenon of perceptual grouping by proximity was investigated. Grouping judgments of random dot patterns were made by the CODE algorithm (van Oeffelen & Vos, 1982) and several related algorithms, and these judgments were compared with subjects’ grouping judgments for the same stimuli. Each algorithm predicted significantly more subject judgments than would be expected by chance. The more subjects agreed on how a given dot pattern should be grouped, the more successful was the algorithms’ ability to match the judgments for that pattern. CODE predicted significantly fewer subject judgments than did some of the other algorithms, largely because of its overemphasis on the extent of interactivity among dots as they are being grouped.     

Common region wins the competition between extrinsic grouping cues: Evidence from a task without explicit attention to grouping

The competition between perceptual grouping factors is a relatively ignored topic, especially in the case of extrinsic grouping cues (e.g., common region or connectedness). Recent studies have examined the integration of extrinsic cues using tasks that induce selective attention to groups based on different grouping cues. However, this procedure could generate alternative strategies for task performance, which are non-related to the perceptual grouping operations. In the current work, we used an indirect task, i.e. repetition discrimination task, without explicit attention to grouping cues to further examine the rules that govern dominance between competing extrinsic grouping factors. This procedure allowed us to obtain an unbiased measure of the competition between common region and connectedness cues acting within the same display. The results corroborate previous data showing that grouping by common region dominated the perceived organization of the display, even though the phenomenological strength of the grouping cues was equated for each participant by means of a preliminary scaling task. Our results highlight the relevance of using indirect tasks as an essential tool for the systematic study of the integration of extrinsic grouping cues.     

Memory for the pitch of a tone

Observers attempted to detect the presence of a pitch difference between two successive tones. The percentage of correct judgments was equivalent for tones separated by .95, 4.5, and 8.9 sec. There was a general increase in reports of a pitch difference with increased intertone interval, which is interpreted as arising from hypothesized shifts in the neural locus of the first stimulus during the intertone interval.     

Memory for the pitch of a tone

Observers attempted to detect the presence of a pitch dirference between two successive tones. The percentage of correct judgments was equivalent for tones separated by 95, 4.5, and 8.9 sec. There was a general increase in reports of a pitch difference with increased intertone interval, which is interpreted as arising from hypothesized shifts in the neural locus of the first stimulus during the intertone interval.     

Sequential reacquisition as a function of timeout from avoidance

Rats learned to reacquire four similar three-member response sequences. Each sequence member was associated with a different response lever, and the correct sequence of levers (i.e., 3-1-2, 2-1-3, 1-3-2, and 2-3-1) changed each session. The first two correct responses of each sequence postponed shock for a fixed period of time. The third correct response initiated a signalled timeout from avoidance. Incorrect responses did not affect the shock interval or reset the sequence. The effects of manipulating timeout duration on the sequential reacquisition baseline were investigated. All subjects displayed biphasic reacquisition performances similar to those controlled by food. The phases were characterized by an initial increase in accuracy, which reached a stable level during the latter portion of each session. Timeout duration affected rate of sequence completion and shock density, but not percentage of errors. Rate of sequence completion was fastest with intermediate timeouts (15 to 60 sec), and slowest with extreme durations (1 or 120 sec). Shock densities peaked with extreme durations and were at minimum with intermediate timeout values. The percentage of errors was the same across timeout durations. These data extend the generality of sequential reacquisition as a procedure for studying learning, and demonstrate timeout from avoidance to be a controlling variable.     

On the surprising salience of curvature in grouping by proximity

The authors conducted 3 experiments to explore the roles of curvature, density, and relative proximity in the perceptual organization of ambiguous dot patterns. To this end, they developed a new family of regular dot patterns that tend to be perceptually grouped into parallel contours, dot-sampled structured grids (DSGs). DSGs are similar to the dot lattices used to study grouping by proximity, except that only one of the potential organizations is rectilinear; the others are curvilinear. The authors used the method of M. Kubovy and J. Wagemans (1995) to study grouping by proximity in DSGs. They found that in the competition between the most likely organizations, one rectilinear and the other curvilinear, the latter is more salient. This phenomenon cannot be explained by contemporary accounts of grouping by proximity or contour integration.     

Discrimination of the order of the components of repeating tone sequences: Effects of frequency separation and extensive practice

The Ss’ task was to identify repeating sequences of pure tones that differed only with respect to the order in which the tones occurred. With tones occurring at a constant rate of 5/sec, performance was better when the tones were widely spaced in frequency than when they were less widely spaced. One S was able, after considerable practice, to distinguish among different sequences whose component tones were presented at rates up to 500/sec. It was tenatively concluded that, in this case, performance was based on temporal (order) information at the slowest presentation rates, primarily on spectral information at the highest rates, and on both order and spectral information at intermediate rates.     

Multistable syllables as enacted percepts: a source of an asymmetric bias in the verbal transformation effect

Perceptual changes are experienced during rapid and continuous repetition of a speech form, leading to an auditory illusion known as the verbal transformation effect. Although verbal transformations are considered to reflect mainly the perceptual organization and interpretation of speech, the present study was designed to test whether or not speech production constraints may participate in the emergence of verbal representations. With this goal in mind, we examined whether variations in the articulatory cohesion of repeated nonsense words--specifically, temporal relationships between articulatory events--could lead to perceptual asymmetries in verbal transformations. The first experiment displayed variations in timing relations between two consonantal gestures embedded in various nonsense syllables in a repetitive speech production task. In the second experiment, French participants repeatedly uttered these syllables while searching for verbal transformation. Syllable transformation frequencies followed the temporal clustering between consonantal gestures: The more synchronized the gestures, the more stable and attractive the syllable. In the third experiment, which involved a covert repetition mode, the pattern was maintained without external speech movements. However, when a purely perceptual condition was used in a fourth experiment, the previously observed perceptual asymmetries of verbal transformations disappeared. These experiments demonstrate the existence of an asymmetric bias in the verbal transformation effect linked to articulatory control constraints. The persistence of this effect from an overt to a covert repetition procedure provides evidence that articulatory stability constraints originating from the action system may be involved in auditory imagery. The absence of the asymmetric bias during a purely auditory procedure rules out perceptual mechanisms as a possible explanation of the observed asymmetries.