Neural encoding of subject-object distance in a visual recognition system

Steroid actions on the vascular wall have been thought to depend on direct, genomic mechanisms being characterized by a considerable delay and on secondary events, including changes of coagulation, plasma lipids, and renal electrolyte and volume regulation. Recently, rapid effects of steroids on the vascular wall have been reported being clearly incompatible with the classical theory of genomic steroid action. As these effects occur in classical target tissues for genomic steroid action, and modulation of intracellular signaling has been shown to influence genomic steroid action, a two-step model of steroid action was developed integrating both genomic and nongenomic aspects and their possible interaction. This review summarizes recent studies on both types of direct, vascular steroid actions, the swift and the sluggish ones, and discusses the role of these actions in regulation of circulatory homeostasis and their potential therapeutic implications.     

Shift of visual fixation dependent on background illumination

Visual fixation, the act of maintaining the eyes directed toward a location of interest, is a highly skilled behavior necessary for high-level vision in primates. In spite of its significance, visual fixation is not well understood; it is not even clear what attributes of the visual input are used to control fixation. Here we show, in four Macaca fascicularis monkeys, that the position the eyes assume during fixation depends on the luminance of the background. Dark background yields fixation positions that are shifted upward with respect to the fixation positions obtained with a dimly illuminated, featureless background. This phenomenon was observed previously in a nutshell by Snodderly; here first we rigorously establish its existence by testing proper controls. We then study the properties of this upshift of the fixation position. We show that, although the size of the upshift varies between monkeys, for all monkeys the upshift is larger than the radius of the fovea. Hence, if the background is dim, the eyes are positioned during fixation so that the target does not fall on the fovea. The size of the upshift remains almost unchanged while the eyes fixate at different orbital positions; thus the upshift is not caused by orbital mechanics. The upshift clearly is present even at the first days of training, but with additional training in fixation with dark background, the upshift increases in size. The upshift rotates with the head. The upshift increases gradually with decreasing levels of background luminosity. Luminosity, not visual contrast, is indeed the primary variable determining the size of the upshift. The contribution of a unit area of the retina to the upshift decreases as inverse square root of distance from the target; therefore, it is the perifoveal region of the retina that mostly contributes to the upshift, while the far periphery has little influence. The upshift can be induced or be canceled in the midst of a fixation by changing the background illumination; hence, the upshift is indeed an attribute of the fixation control system. Finally, the fixation-upshift studied here is different from a previously reported upshift of the endpoints of memory-guided saccades with respect to their target locations. These two types of upshift add up to each other. In discussing the function of the upshift, we note a possible morphological analogue with the retinal rod distribution. The upshift moves the line of gaze to a point intermediate between the fovea and the "dorsal rod peak." The upshift thus may improve visual acuity in scotopic conditions. The brain structure in which the upshift is generated must be involved in both ocular control and visual sensation. We consider several possibilities, of which we regard as the most likely the cerebellum and superior colliculus.     

Feeding-based arousal effects on visual recognition memory in early infancy.

Arousal effects on a 1-trial visual recognition paired-comparison task were studied at newborn, 1-month, and 4-month test ages. Infants were tested before and after feeding, with arousal assumed to be lower after feeding. Newborns and 1-month-olds shifted from a familiarity preference before feeding to a novelty preference after feeding. A control group tested only after feeding confirmed that this shift was not due to increased stimulus exposure from the prefeeding test. By 4 months, infants showed novelty preferences independent of feeding. This age by arousal interaction for recognition memory extends previous knowledge by including endogenous arousal with age, stimulus, and length of exposure as contributors to familiarity–novelty preferences. It also extends and provides converging evidence for arousal effects on visual attention in early infancy found previously with preferential looking. A shift from subcortical to cortical dominance is supported. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effects of foveal load and visual context on peripheral letter recognition

Peripheral letter recognition was examined by presenting subjects with a letter triad centered 7.16 degrees to the right of fixation. At the same time, a single letter was presented at the point of fixation that was either the same as one of the letters in the triad or different from any of the triad letters. On other trials, no letter was presented at the point of fixation. Results supported and extended previous foveal load research. The disruptive effect of foveal load does not depend solely on the presence or absence of a foveal stimulus. Recognition of the first letter in non-words was disrupted when a foveal letter was presented that was different from the peripheral letter. Recognition of the middle letter for both words and non-words was disrupted when a foveal letter was presented that was the same as the middle letter. A significant interaction between foveal letter and triad type was also found. No evidence was found to suggest that recognition of a peripheral letter is significantly better when that same letter is also present at the point of fixation.     

Phonological effects in visual word recognition: Investigating the impact of feedback activation.

P. M. Pexman, S. J. Lupker, and D. Jared (2001) reported longer response latencies in lexical decision tasks (LDTs) for homophones (e.g., maid) than for nonhomophones, and attributed this homophone effect to orthographic competition created by feedback activation from phonology. In the current study, two predictions of this feedback account were tested: (a) In LDT, observe homophone effects should be observed but not regularity or homograph effects because most exception words (e.g., pint) and homographs (e.g., wind) have different feedback characteristics than homophones do, and (b) in a phonological LDT ("does it sound like a word?"), regularity and homograph effects should be observed but not homophone effects. Both predictions were confirmed. These results support the claim that feedback activation from phonology plays a significant role in visual word recognition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Priming the visual recognition of spoken words

A preliminary investigation was conducted to understand the effects of word visibility and prime association factors on visual spoken word recognition in lipreading, using a related/ unrelated prime-target paradigm. Prime-target pairings were determined on the basis of paper-and-pencil word associations completed by 85 participants with normal hearing. Spoken targets included 60 single-syllable Modified Rhyme Test words, prerecorded on laser video disc. Participants included 20 individuals with normal hearing and at least average lipreading skill for sentence-length materials. In related prime-target pairings, more targets with a high prime association were identified than with a low prime association. In unrelated prime-target pairings, a larger number of more-visible than less-visible targets was correctly identified. Individual participant differences were not statistically significant. Results from the present study suggest implications for models of visual spoken word recognition.     

Textons, visual pop-out effects, and object recognition in infancy.

Five experiments were conducted to determine whether primitive perceptual features, or textons, which B. Julesz (1984) identified in studies of texture segregation with adults, also affect object recognition early in development. Three-month-old infants discriminated Ts and Ls composed of overlapping line segments from +s but not from each other in a delayed-recognition test after 24 hrs; however, Ts and Ls were discriminated from each other after only 1 hr. In a priming paradigm, Ts, Ls, and +s were discriminated from one another after 2 wks. In succeeding experiments, infants exhibited adultlike visual pop-out effects in both delayed recognition and priming paradigms, detecting an L in the midst of 6 +s and vice versa; these effects were symmetrical. The pop-out effects apparently resulted from parallel search: Infants failed to detect 3 Ls among 4 +s. Clearly, some of the same primitive units that have been identified as the building blocks of adult visual perception underlie object recognition early in infancy. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Suedohomofoan effects in visual word recognition: Evidence for phonological processing.

Investigated the pseudohomophone effect, which is considered to be evidence that phonological recoding occurs in the lexical decision task in which a letter string like brane is identified as a nonword. 22 undergraduates read 156 letter strings, half of which were words, and identified them as words or nonwords. Half of the nonwords were pseudohomophones like brane, which sounds like a real word but is not spelled like one; half were strings like slint, which neither looks nor sounds like a real word. Response time to pseudohomophones was slower than response time to other nonwords. The interpretation of this result is that the letter string brane is transformed into a phonological code that accesses the entry for brain in a phonological lexicon, thus necessitating a time-consuming spelling check to avoid making a false positive response. Since letter strings like slint have no lexical entries, a postaccess spelling check is not necessary. Thus, the pseudohomophone effect reflects phonological processing. (French abstract) (11 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Context effects in visual word recognition: lexical relatedness and syntactic context

In three experiments, we investigated how associative word-word priming effects in German depend on different types of syntactic context in which the related words are embedded. The associative relation always concerned a verb as prime and a noun as target. Prime word and target word were embedded in visually presented strings of words that formed either a correct sentence, a scrambled list of words, or a sentence in which the target noun and the preceding definite article disagreed in syntactic gender. In contrast to previous studies (O'Seaghdha, 1989; Simpson, Peterson, Casteel, & Burgess, 1989), associative priming effects were not only obtained in correct sentences but also in scrambled word lists. Associative priming, however, was not obtained when the definite article and the target noun disagreed in syntactic gender. The latter finding suggests that a rather local violation of syntactic coherence reduces or eliminates word-word priming effects. The results are discussed in the context of related work on the effect of gender dis-/agreement between a syntactic context and a target noun.     

A comparison of the effects of depth rotation on visual and haptic three-dimensional object recognition.

A sequential matching task was used to compare how the difficulty of shape discrimination influences the achievement of object constancy for depth rotations across haptic and visual object recognition. Stimuli were nameable, 3-dimensional plastic models of familiar objects (e.g., bed, chair) and morphs midway between these endpoint shapes (e.g., a bed–chair morph). The 2 objects presented on a trial were either both placed at the same orientation or were rotated by 90° relative to each other. Discrimination difficulty was increased by presenting more similarly shaped objects on mismatch trials (easy: bed, then lizard; medium: bed, then chair; hard: bed, then bed–chair morph). For within-modal visual matching, orientation changes were most disruptive when shape discrimination was hardest. This interaction for 3-dimensional objects replicated the interaction reported in earlier studies presenting 2-dimensional pictures of the same objects (Lawson & Bülthoff, 2008). In contrast, orientation changes and discrimination difficulty had additive effects on within-modal haptic and cross-modal visual-to-haptic matching, whereas cross-modal haptic-to-visual matching was orientation invariant. These results suggest that the cause of orientation sensitivity may differ for visual and haptic object recognition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Transformations in the recognition of visual forms.

Conducted 3 experiments in which Ss were required to learn to recognize 4 flexible plastic shapes photographed on different backgrounds from different angles. Slides were designated as either prototypes (photographed from overhead on a black background), cued (photographed from many angles on a definite background, e.g., a chair), or uncued (the cued photographs placed on a black background). Ss were 80 undergraduates in Exp I, 80 16-24 yr olds in Exp II, and 43 undergraduates in Exp III. Variables investigated were (a) order, amount, and type of training (prototype, cued, or uncued); (b) type of training instructions (Ss were told either that there were 4 classes of objects or 4 objects viewed from various backgrounds); and (c) presence or absence of context in training or testing (background which gave cues to transformation). Results indicate that (a) type of training had a significant effect on performance; (b) the presentation of uncued test slides before cued ones decreased performance on the cued slides, while cued slides presented first facilitated performance on the uncued slides; and (c) the presence of context in training significantly increased rates of pattern learning and success in recognizing new material. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Additive and interactive effects on response time distributions in visual word recognition.

Across 3 different word recognition tasks, distributional analyses were used to examine the joint effects of stimulus quality and word frequency on underlying response time distributions. Consistent with the extant literature, stimulus quality and word frequency produced additive effects in lexical decision, not only in the means but also in the shape of the response time distributions, supporting an early normalization process that is separate from processes influenced by word frequency. In contrast, speeded pronunciation and semantic classification produced interactive influences of word frequency and stimulus quality, which is a fundamental prediction from interactive activation models of lexical processing. These findings suggest that stimulus normalization is specific to lexical decision and is driven by the task's emphasis on familiarity-based information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differential age effects for case and hue mixing in visual word recognition.

The authors compare older adults' lexical-decision data with younger adults' data reported in P. Allen, A. F. Smith, et al. (2002). On the basis of their work, it was proposed that consistent-case words would be processed by the faster holistic (magnodominated) stream, but that mixed-case words would be processed by the slower analytic (interblob-dominated or blob-dominated) streams. Hue mixing was predicted to have no effect on consistent-case performance, but mixed-hue/mixed-case words were predicted to be recognized faster than monochrome/mixed-case words. Younger adults showed the predicted results, but older adults did not. These results suggest that holistic central processes are maintained, but that older adults exhibited an analytic decrement. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Adult age differences in the effects of sentence context and stimulus degradation during visual word recognition.

I investigated adult age differences in the efficiency of feature-extraction processes during visual word recognition. Participants were 24 young adults (M age?=?21.0 years) and 24 older adults (M age?=?66.5 years). On each trial, subjects made a word/nonword discrimination (i.e., lexical decision) regarding a target letter-string that was presented as the final item of a sentence context. The target was presented either intact or degraded visually (by the presence of asterisks between adjacent letters). Age differences in lexical decision speed were greater for degraded targets than for intact targets, suggesting an age-related slowing in the extraction of feature-level information. For degraded word targets, however, the amount of performance benefit provided by the sentence context was greater for older adults than for young adults. It thus appears that an age-related deficiency at an early stage of word recognition is accompanied by an increased contribution from semantic context. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dissociative effects of stimulus quality on semantic and morphological contexts in visual word recognition.

Semantic and morphological contexts were manipulated jointly with stimulus quality under conditions where there were few related prime-target pairs (i.e., low relatedness proportion) in a lexical decision experiment. Additive effects of semantic context and stimulus quality on RT were observed, replicating previous work. In contrast, morphological context interacted with stimulus quality. This dissociation is discussed in the context of Besner and colleagues' evolving multistage framework. The essence of the account is that 1) stimulus quality affects feature and letter levels, but not later levels, 2) feedback from semantics to the lexical level is inoperative under low relatedness proportion conditions (hence stimulus quality and semantic context yield additive effects), whereas 3) feedback from the lexical level to the letter level is intact, hence stimulus quality and morphological context produce an interaction by virtue of them affecting a common stage of processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Frequency effects in spoken and visual word recognition: Evidence from dual-task methodologies.

The authors report 3 dual-task experiments concerning the locus of frequency effects in word recognition. In all experiments, Task 1 entailed a simple perceptual choice and Task 2 involved lexical decision. In Experiment 1, an underadditive effect of word frequency arose for spoken words. Experiment 2 also showed underadditivity for visual lexical decision. It was concluded that word frequency exerts an influence prior to any dual-task bottleneck. A related finding in similar dual-task experiments is Task 2 response postponement at short stimulus onset asynchronies. This was explored in Experiment 3, and it was shown that response postponement was equivalent for both spoken and visual word recognition. These results imply that frequency-sensitive processes operate early and automatically. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Homophone effects in visual word recognition depend on homophone type and task demands.

This experiment examined how the characteristics of homophones and their mates influence homophone effects, as a function of task demands. Two types of homophones were presented: 1) low-frequency homophones with higher-frequency mates that are not animal names (e.g., maid--made), and 2) low-frequency homophones with mates that are, on average, of equivalent frequency and are animal names (e.g., foul--fowl). We observed a double dissociation: In the lexical decision task (LDT), there was a homophone effect for the first type of homophones but not for the second, whereas in the semantic categorization task (SCT) the opposite was true. These results suggest that in these tasks the effects of homophony arise when the homophone's mate creates competition in terms of the type of processing emphasized in the task, namely, orthographic processing in the LDT and semantic processing in the SCT. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Behavioral and neural effects of chromatic isoluminance in the primate visual motion system

We have previously reported that the responses of individual neurons in macaque visual area MT elicited by movement of contrast-reversing heterochromatic red/green borders are largest when the two hues are "balanced" or isoluminant (Dobkins & Albright, 1994). This "neural" isoluminant point was found to vary somewhat across the sample of neurons. Here, we compare the average neural isoluminant point in area MT to a behavioral measure of isoluminance, obtained using a modification of an oculomotor procedure developed by Chaudhuri and Albright (1992). These behavioral estimates of isoluminance closely parallel the neuronal data obtained from area MT. In accordance with previous evidence (e.g. Lee et al., 1988; Kaiser et al., 1990; Valberg et al., 1992), this correlation suggests that activity within the dorsal/magnocellular stream underlies behavioral expression of chromatic isoluminance.