Reflexive Attention Modulates Processing of Visual Stimuli in Human Extrastriate Cortex

Attention can be oriented reflexively to a location in space by an abrupt change in the visual scene. In the present study, we investigated the consequences of reflexive attention on the neural processing of visual stimuli. The findings show that reflexively oriented attention produces modulations in early sensory analysis at the same extrastriate neural locus as the earliest effects of voluntarily focused attention. In addition, stimulus processing was found to be enhanced at later stages of analysis, which reflect stimulus relevance. As is the case with behavioral measures of reflexive attention, these physiological enhancement effects are rapidly engaged but short-lived. As time passes between the initial attention-capturing event and subsequent stimuli, the extrastriate effect reverses, and the enhancement of higher order processing subsides. These findings indicate that reflexive attention is able to affect perceptions of the visual world by modulating neural processing as early as extrastriate visual cortex.     

Orientation Constancy in Neurons of Monkey Visual Cortex

We studied the effect of body tilt on the orientation selectivity of single neurons in the visual cortex of an alert monkey. The monkey performed a visual fixation task either in the upright position or with its whole body tilted about the naso-occipital (roll) axis by ±25° or ±30°. We determined the preferred stimulus orientation for 51 of 117 neurons in two or, if possible, three body positions (i.e. with the whole body upright, and tilted either left ear or right ear down). In striate cortex, most of the neurons were of a non-compensatory type, showing a change in the preferred orientation according to the body tilt and the estimated counterrolling of the eye. By contrast, about 40% of the neurons in prestriate cortex were of a compensatory type, preferring similar orientations in all body positions. This suggests that mechanisms which produce orientation constancy with respect to the direction of gravity are implemented at an early stage of cortical processing.     

Alteration of Auditory Cortex Activity with a Visual Stimulus through Conditioning: A 2-Deoxyglucose Analysis

In two experiments, the 2-deoxyglucose metabolic mapping technique was used to examine the hypothesis that a stimulus of one modality (a light) will begin to activate the sensory cortex of a stimulus of another modality (a tone) with which it has been repeatedly paired. Adult gerbils received repeated presentations of either a light or the light paired with a tone known to affect 2DG labeling patterns in the auditory cortex. Intermittent footshock was included on a pseudo-random basis to maintain arousal in the subjects. One day after training, each gerbil was injected with 2DG and either received repeated presentations of the light only or was simply exposed to the training context. Analysis of the auditory cortex revealed no differences in overall metabolic activity of the auditory cortex between the groups. However, in both experiments, the light that was previously paired with the tone changed the relative activity of the cortical subfields compared to the light not previously paired with the tone. Specifically, the results indicate greater activity in the anterior auditory field (AAF—Experiments 1 and 2) and the posterior fields (DPVP—Experiment 2) relative to the primary field AI in response to the light that was previously paired with the tone during training. Gerbils either only placed in the context during the 2DG session or that received unpaired presentations of the light and tone during training did not show this shift in relative labeling between the subfields. Because no differences in overall activity of the auditory cortex were found, we conclude that the shift in relative labeling between the subfields reflects, on average, both an increase in activity of fields AAF and DPVP and a concomitant decrease in AI activity in response to the light stimulus. The results have implications for our understanding both of brain learning mechanisms in general and the potential functions of auditory cortex subfields in particular.     

Representations in the Human Prefrontal Cortex

ABSTRACT— The prefrontal cortex (PFC) in humans has been studied for more than a century, but many crucial questions about its functions remain unanswered. This paper will highlight a few key differences between human and animal PFCs, and between the human PFC (HPFC) and other parts of the human brain. We then make a case that the HPFC is critically important for executing behaviors over time and integrating disparate information from throughout the brain. Finally, we will focus on our position in the current debate regarding how the HPFC performs its functions and discuss future directions for research.     

The Delay in Visual Reorientation following Exposure to a Change in Direction of Resultant Force on a Human Centrifuge

Errors in reporting a cued target letter appearing among a string of letters more often reflect the mislocation of a letter appearing elsewhere in the string than the intrusion of one not in the string. The current experiment was conducted to determine the representation of letters at the stage at which errors occur. Four letters (from a set of 12 chosen to contain counterpart pairs that were similar physically, phonemically, or both physically and phonemically) appeared in each exposure, with the target letter indicated by a cue in the postexposure mask. Letter strings presented to one group of subjects were flanked on either side by a pound sign (#) to assess the effect of lateral masking on the terminal letter in the string. Physical similarity dictated the pattern of mislocations between counterparts, suggesting a physical rather than phonemic or abstract representation. Lateral masking played no significant role in the difference between intrusions and mislocations.     

The Functions of the Visual Cortex in Optic Nystagmus at Different Velocities of Movement in the Visual Field

(Sherif, M., and Sherif, C. W. Groups in Harmony and Tension. New York: Harper, 1953. Pp. 316.), Philander Smith College, Little Rock, Arkansas Reviewed by Martin M. Grossack.     

A System for Relational Reasoning in Human Prefrontal Cortex

The integration of multiple relations between mental representations is critical for higher level cognition. For both deductive- and inductive-reasoning tasks, patients with prefrontal damage exhibited a selective and catastrophic deficit in the integration of relations, whereas patients with anterior temporal lobe damage, matched for overall IQ but with intact prefrontal cortex, exhibited normal relational integration. In contrast, prefrontal patients performed more accurately than temporal patients on tests of both episodic memory and semantic knowledge. These double dissociations suggest that integration of relations is a specific source of cognitive complexity for which intact prefrontal cortex is essential. The integration of relations may be the fundamental common factor linking the diverse abilities that depend on prefrontal function, such as planning, problem solving, and fluid intelligence.     

Using Neuroimaging to Measure Mental Representations: Finding Color-OpponentNeurons in Visual Cortex

To date, most neuroimaging studies have tried to localize large regions in the brain that are responsible for specific behaviors or mental operations. Psychological theory, however, is more concerned with the nature of mental functions than with the locations of their neural substrates. This article reviews work that moves beyond functional anatomy to measure how color is represented by neurons in visual cortex. The general approach has three basic steps: First, the areas under investigation are localized in the brain. Second, responses of these areas are measured to sets of systematically varying stimuli, designed to uncover the nature of cortical representations. Third, the neuroimaging data are compared with behavioral data measured with the same stimuli. Results obtained using this approach support the hypothesis that primary visual cortex contains color-opponent neurons that support perception.     

顶叶在特征捆绑中的作用--对一例典型双侧顶叶损伤病人的研究

本实验以一例典型双侧顶叶损伤患者为研究对象,以数字和几何形状为材料,采用形状和颜色特征识别任务,主要考察了顶叶及空间信息是否影响视觉特征捆绑。结果显示,患者在特征捆绑任务上操作成绩较差,错觉性结合错误远远多于特征错误,且正确反应及错觉性结合受刺激间的距离及呈现方式的影响,表现出距离和位置效应。这些结果表明,顶叶在视觉特征捆绑中起重要作用,这种影响作用很可能与空间注意有关。本研究进一步为特征整合理论提供了神经心理学的证据。     

Neurons in Human Temporal Cortex Active with Verbal Associative Learning

In neuronal activity recorded from human middle temporal gyrus during learning of associations between word pairs, a population was identified that had greater activity for associations that were learned rapidly during initial encoding compared to those learned slowly or not at all by an individual subject. This population can be separated from other neurons by the combination of inhibition during word reading when no learning is required and excitation during recent memory for words. These neurons are present in both hemispheres, predominately in deeper layers of cortex. During initial encoding, the increased activity appears at presentation of all word pairs but persists for several seconds only for the rapidly learned pairs, likely reflecting rehersal of items being learned. Human associative learning is related to activity of this specific population of “association” neurons, identified here for the first time.     

Tonic Activity Level in the Right Prefrontal Cortex Predicts Individuals' Risk Taking

ABSTRACT— Human risk taking is characterized by a large amount of individual heterogeneity. In this study, we applied resting-state electroencephalography, which captures stable individual differences in neural activity, before subjects performed a risk-taking task. Using a source-localization technique, we found that the baseline cortical activity in the right prefrontal cortex predicts individual risk-taking behavior. Individuals with higher baseline cortical activity in this brain area display more risk aversion than do other individuals. This finding demonstrates that neural characteristics that are stable over time can predict a highly complex behavior such as risk-taking behavior and furthermore suggests that hypoactivity in the right prefrontal cortex might serve as a dispositional indicator of lower regulatory abilities, which is expressed in greater risk-taking behavior.     

The Effects of Acute Aerobic Exercise on the Primary Motor Cortex

ABSTRACT. The effect of aerobic exercise on primary motor cortical excitability is a relevant area of interest for both motor learning and motor rehabilitation. Transient excitability changes that may follow an exercise session are a necessary precursor to more lasting neuroplastic changes. While the number of studies is limited, research suggests that a session of aerobic exercise can create an ideal environment for the early induction of plasticity. Potential mechanisms include the upregulation of neurotransmitter activity, altered cerebral metabolism and cortisol levels, and increases in brain-derived neurotrophic factor. While there is considerable evidence that chronic physical activity positively impacts brain health and function, studies examining cortical excitability changes and motor performance after a single session of exercise are lacking. Further research is required to determine the clinical utility and feasibility of aerobic exercise.     

Reinforcement Probability and Delay as Determinants of Human Impulsiveness

In behavior theory, “impulsiveness” refers to the choice of an immediate, small reinforcer over a delayed, large reinforcer. Such behavior generally is attributed to a reduction in the value of the large reinforcer as a function of the duration of delay. In contrast, social learning theorists have suggested that human impulsiveness can result from a lowered “expectancy” (subjective probability) of reinforcement. Effects of probability and delay were assessed by asking adults to make repeated choices between reinforcement schedules in which the reinforcers were slides of entertainment figures. An immediate, 5-s reinforcer was consistently chosen over an immediate, 40-s reinforcer if the probability of receiving the large reinforcer had previously been low (.20), implying that impulsiveness can occur without time-based discounting. However, reinforcement delay was also influential: Choice between a certain, small reinforcer and an uncertain, large reinforcer varied according to which reinforcer was immediate and which delayed.

     

Adult's Eyes Trigger Shifts of Visual Attention in Human Infants

Two experiments examined whether infants shift their visual attention in the direction toward which an adult's eyes turn. A computerized modification of previous joint-attention paradigms revealed that infants as young as 3 months attend in the same direction as the eyes of a digitized adult face. This attention shift was indicated by the latency and direction of their orienting to peripheral probes presented after the face was extinguished. A second experiment found a similar influence of direction of perceived gaze, but also that less peripheral orienting occurred if the central face remained visible during presentation of the probe. This may explain why attention shifts triggered by gaze perception have been difficult to observe in infants using previous naturalistic procedures. Our new method reveals both that direction of perceived gaze can be discriminated by young infants and that this perception triggers corresponding shifts of their own attention.     

Classical Delay Eyeblink Conditioning in in 4- and 5-Month-Old Human Infants

Abstract-Simple delay classical eyeblink conditioning, using a tone conditioned stimulus (CS) and airpuff unconditioned stimulus (US), was studied in cross-sectional samples of 4- and 5-month-old healthy, full-term infants. Infants received two identical training sessions, 1 week apart. At both ages, infants experiencing paired tones and air-puffs demonstrated successful conditioning over two sessions, relative to control subjects who had unpaired training. Conditioning was not evident, however, during the first session. Two additional groups of 5-month-olds received varied experiences during Session 1, either unpaired presentations of the CS and US or no stimulus exposure, fol-lowed by paired conditioning during Session 2. Results from these groups suggest that the higher level of conditioning observed following two sessions of paired conditioning was not the result of familiarity with the testing environment or the stimuli involved but, rather, the result of retention of associative learning not expressed during the first conditioning session.