Giotto's applications of embodied perception: Lateral and vertical dimensions of space.

Giotto's Arena Chapel frescoes, dating from the early fourteenth century, provide salient illustrations of two types of embodied perceptions. One is universal, a consequence of biology and the physical laws of nature, linked to the vertical dimension of space, and impacting on affect and moral judgement. The other is culturally determined, acquired from the direction of reading script and affecting perceptions of directions of movement, time and causality. Giotto's intuitive use of embodiments, the result of a newly evolving realism in painting, may have prompted late mediaeval chapel-visitors to empathize with the storied biblical characters, so that figures that were once only the object of religious veneration and awe were now made into living beings with a shared humanity, resulting in an awakening of a personal agency that fueled the Renaissance and Modernism.

Obsessive-compulsive disorder patients display enhanced latent inhibition on a visual search task.

Latent inhibition (LI) is a phenomenon that reflects the ability to ignore irrelevant stimuli. LI is attenuated in some schizophrenic patient groups and in high schizotypal normal participants. One study has found enhanced LI in patients with obsessive-compulsive disorder (OCD [Swerdlow, N. R., Hartston, H. J., & Hartman, P. L., 1999. Enhanced visual latent inhibition in obsessive-compulsive disorder. Biological Psychiatry, 45, 482-488]). The present experiment replicated this finding using a within-subject visual search LI task, with OCD patients displaying more LI than healthy controls. The contrasting LI effects in schizophrenia and OCD are discussed in terms of how these groups differentially process relevant and irrelevant stimuli, and how that outcome affects subsequent behavior.

Construct validity of the animal latent inhibition model of selective attention deficits in schizophrenia.

Latent inhibition (LI) is demonstrated when a previously unattended/inconsequential stimulus is less effective in a new learning situation than a novel stimulus. In rats and humans, LI is reduced by dopamine agonists and increased by dopamine antagonists. In addition, LI is attenuated in actively psychotic schizophrenia patients, thus conferring strong predictive validity to the animal LI preparation for schizophrenia. However, the validity of the attentional construct in the LI model of schizophrenia dysfunction depends on confirming two assumptions: that animal and human LI share a common process, and that the process is related to selective attention. Evidence to support both assumptions is presented, followed by a description of a conditioned attention theory that emphasizes the role of initial levels of attention elicited by repeated relevant and irrelevant stimuli, and the differences between these levels in schizophrenia and normal groups.

The visual search analogue of latent inhibition: implications for theories of irrelevant stimulus processing in normal and schizophrenic groups.

Latent inhibition (LI) is a robust phenomenon that is demonstrated when a previously inconsequential stimulus is less effective in a new learning situation than a novel stimulus. Despite LI's simplicity, there is considerable disagreement as to its theoretical basis. Attentional theories claim that unattended stimulus preexposures reduce stimulus associability. Alternatively, it has been asserted that associability is unaffected and that LI is a result of competition/retrieval processes. The present article reviews a series of visual search studies, some with normal subjects, both undifferentiated and divided into low and high schizotypals, and others with pathologies that entail dysfunctional attention, such as schizophrenia, Parkinson's disease, and anxiety. The visual search conditions were designed to model those of traditional LI experiments, while tapping attentional processes independently of the learning scores that index LI. A variety of evidence from these and other studies is used to support the involvement of attentional and retrieval processes in LI. A model of the mechanism of action of these processes in LI is presented, together with its application to schizophrenia.

There is a time and a place for everything: bidirectional modulations of latent inhibition by time-induced context differentiation.

Latent inhibition (LI) is defined as poorer evidence of learning with a stimulus that previously was presented without consequence, as compared with a novel or previously attended stimulus. The present article reviews the evidence, mostly from three-stage conditioned taste aversion studies (preexposure, conditioning, and test), that LI can be either attenuated or enhanced depending on the length of the retention interval between conditioning and test and where that interval was spent. Time-induced reduction in LI is observed when the interval context is the same as that of the preexposure, conditioning, and test stages. Super-LI is obtained when a long retention interval is spent in a context that is different from that of the other stages. The differential modulations of LI appear to be the result of the strengthening of primacy effects (i.e., first training disproportionately stronger than subsequent training) by long-interval different contexts, thereby producing super-LI, and the reversal of this effect by long-interval same contexts, thereby producing attenuated LI. The bidirectional effects of time/ context modulations on LI, unaccounted for by current learning theories, are explained, in part, by a time-induced context differentiation process. Implications for theories of LI, learning, and, memory are discussed.

Latent inhibition and asymmetrical visual-spatial attention in children with ADHD.

The research was designed to determine whether the purported hemispheric asymmetries that are associated with attention deficit/hyperactivity disorder (ADHD) affect performance on a selective attention visual search task, and whether any obtained asymmetry will be modulated by methylphenidate. Two groups of children (8-15 years) with ADHD, one with methylphenidate treatment (ADHD+) and one without (ADHD+), were compared to matched controls on a two-stage visual search task. The task assessed right-left visual field asymmetries and the effects of changing a previous distractor into a target. Such a procedure, related to latent inhibition (LI; poorer performance to a previously irrelevant stimulus than to a novel one), can provide evidence for dysfunctional processing of irrelevant stimuli. All three groups exhibited the LI effect. The ADHD group, however, exhibited less LI for left- than right-side targets, an effect absent in the control and ADHD+ groups, suggesting a lateralized attentional deficit for ADHD+ that was normalized by methylphenidate.

Amphetamine-produced attenuation of latent inhibition is modulated by stimulus preexposure duration: implications for schizophrenia.

The relationship between amphetamine-produced dopamine overreactivity and attention to irrelevant stimuli is reflected in an attenuated latent inhibition (LI) effect. This occurs in both animal and human subjects. The present study examines the manner in which this effect in rats is modulated by the duration of stimulus preexposure. A factorial design was used with three levels of stimulus preexposure duration and either amphetamine or saline administration. In addition, there were corresponding groups that did not receive stimulus preexposure. It was found that although amphetamine did indeed abolish LI at short exposure intervals (30 sec), the LI effect was normal for long stimulus preexposure durations (150 sec). The data were discussed in terms of the affects of amphetamine on the processing of irrelevant stimuli and the relationship of such a dysfunctional attentional process to schizophrenia.

Latent inhibition in humans: data, theory, and implications for schizophrenia.

Learning about the consequences of a stimulus is retarded if that stimulus has been experienced without reinforcement. A literature review of this latent inhibition (LI) effect indicates that LI is similar in human and other species, although in adult humans it often requires a masking or distracter task. The discrepancy in conditions for producing LI can be accounted for by developmental differences in the automatic processing of unattended stimuli. In adults, automatic processes are subject to a controlled information-processing override. Masking prevents controlled processing of the preexposed stimuli so that they remain unattended. The role of masking in attenuating LI in schizotypal/schizophrenic groups is assessed. It is proposed that schizophrenia is related to an inability to use occasion-setting properties of context or to switch from controlled to automatic processing of inconsequential events.

Abolition of the expression but not the acquisition of latent inhibition by chronic amphetamine in rats.

The animal amphetamine model of schizophrenia has been based primarily on stereotyped behavior. The present study sought to demonstrate an amphetamine-induced deficit in attentional processes. To this end, the effects of acute and chronic (14 days) 1.5 mg/kg dl-amphetamine administration on the ability of rats to ignore irrelevant stimuli were examined using the paradigm of latent inhibition (LI) in a conditioned emotional response (CER) procedure. The procedure consisted of three stages: pre-exposure, in which the to-be-conditioned stimulus, tone, was presented without being followed by reinforcement; acquisition, in which the pre-exposed tone was paired with shock; and test, in which LI was indexed by animals' suppression of licking during tone presentation. Experiment 1 showed that chronic but not acute treatment abolished LI. Experiment 2 showed that animals receiving chronic amphetamine pretreatment but pre-exposed and conditioned without the drug, exhibited normal LI. In Experiment 3, animals which received chronic amphetamine pretreatment and were pre-exposed under the drug but conditioned without it, also showed normal LI. The implications of these results for the animal amphetamine model of schizophrenia are discussed.

The abolition of the partial reinforcement extinction effect (PREE) by amphetamine.

The effects of amphetamine administration on the partial reinforcement extinction effect (PREE) at one trial a day, were examined. Two groups of rats were trained to run in a straight alley. The continuously reinforced (CRF) group received food reward on every trial. The partially reinforced (PRF) group was rewarded on a quasirandom 50% schedule. All animals were then tested in extinction. dl-Amphetamine 1.5 mg/kg was administered in a 2 X 2 design, i.e., drug-no drug in acquisition and drug-no drug in extinction. The PREE, i.e., increased resistance to extinction exhibited by PRF animals as compared to CRF animals, was obtained in animals that received saline in acquisition, independently of drug treatment in extinction. In contrast, amphetamine administered in acquisition abolished the PREE irrespective of drug treatment in extinction. In addition, amphetamine administered in extinction alone increased resistance to extinction in PRF animals.

Visual search in schizophrenia: latent inhibition and novel pop-out effects.

A visual search task was used to assess attentional function in a mixed group of schizophrenic patients and in normal controls. Subjects identified presence or absence of a unique shape presented with homogeneous distractors. Response time (RT) was examined as a function of prior experience with target, distractor, or both. On each trial, targets and/or distractors were either novel or familiar. Schizophrenic patients were slower than controls in all conditions. In the test phase, three target/distractor conditions were examined (PE - target and distractors pre-exposed but reversed; NPE - target novel and distractors pre-exposed; NOV - novel target and distractors). As predicted, normal controls, but not schizophrenics, showed latent inhibition (LI: PE minus NPE). The latter finding was due to the absence of normal LI in female patients. A novel pop-out effect (NOV minus NPE) was obtained which did not interact with any of the other variables. The results suggest that the LI effect is indeed related to the processing of irrelevant stimuli, and that, at least female schizophrenic patients process such stimuli differently from controls. Past inconsistencies in the LI-schizophrenia literature may be the result of disproportionate gender compositions in patient and control groups.

Performance on the visual search analog of latent inhibition is modulated by an interaction between schizotypy and gender.

Two experiments examined the visual search analog of latent inhibition (LI) and the novel popout (NPO) effect in healthy humans. In Experiments 1 (n=48) and 2 (n=180), subjects judged the positions (left or right side of a computer screen) of a unique target amongst a field of homogeneous distractors. In both experiments, there was a strong LI effect, as indicated by longer response times (RT) to those displays in which the target was previously a distractor and the distractors were previously the target, as compared with displays in which the target was novel and the distractors were previously the target. NPO, faster RT to a display in which the target was novel on a background of familiar distractors than to a display in which both target and distractors were novel, was not obtained. In Experiment 1, LI magnitude was not affected by gender. In Experiment 2, LI magnitude was larger for low schizotypal females than for high schizotypal females, a result not obtained for males. This pattern is similar to one reported for medicated schizophrenic out-patients (Lubow, R.E., Kaplan, O., Abramovich, P., Rudnick, R., Laor, N., 2000. Visual search in schizophrenics: latent inhibition and novel popout effects. Schizophr. Res., in press). Together, these data suggest that the LI deficits found in high schizotypal healthy subjects and in schizophrenic patients represent a dysfunction that is characterized by an inability to reduce attention allocated to irrelevant stimuli, and that this may serve as a trait marker for some subtypes of schizophrenia, particularly those associated with female gender.

Latent inhibition deficits in high-schizotypal normals: symptom-specific or anxiety-related?

Latent inhibition (LI) is the phenomenon in which subjects who have repeatedly experienced an irrelevant stimulus perform more poorly on a new learning task with that stimulus than with a novel stimulus, presumably because of a decline in stimulus-specific attention. The present article reviews the literature on LI deficits in high-schizotypal normal subjects and schizophrenic patients. Although LI-deficits have been thought to be specific to these groups, evidence is presented that the effects may be related to the anxiety components of high-schizotypality and related pathologies.

Latent inhibition effects reflected in event-related brain potentials in healthy controls and schizophrenics.

The present study examined the effects of pre-exposure of an irrelevant stimulus on reaction time and the contingent negative variation (CNV) in healthy controls and schizophrenic patients. In Phase I, subjects were either pre-exposed (PE) or not pre-exposed (NPE) to repeated presentations of an auditory probe stimulus (white noise), while engaged in counting auditory nonsense syllables. In Phase II, all subjects were required to produce a rapid motor response to a visual imperative stimulus that was preceded by the previously irrelevant auditory stimulus. During Phase II in controls, for PE as compared to NPE subjects, the build-up of CNV across trials was delayed. In schizophrenics, for both PE and NPE subjects, there was no pre-exposure effect on the CNV component. These findings indicate that ERPs may be useful in explicating the normal latent inhibition effect (poor associative learning to a stimulus after it has been passively pre-exposed) and its disruption in schizophrenia.

Latent inhibition as a measure of learned inattention: some problems and solutions.

The latent inhibition (LI) paradigm has been used to assess attentional dysfunction in various pathological groups. The rationale is based on the assumption that passive stimulus exposure results in the acquisition of an inattentional response to that stimulus. Consequently, compared to a novel stimulus in the same new learning situation, the preexposed stimulus is at a disadvantage. It is argued that methodological and conceptual problems in constructing procedures and designs have created obstacles in relating disrupted LI to psychopathology. Specifically, issues associated with within- and between-subject designs, dichotomous dependent variables, ceiling effects, converging operations, and possible mis-attribution of the LI effect are addressed. Designs and data from several new human-LI paradigms, with normal, de novo Parkinson, and schizophrenic subjects are examined. Results from a multi-condition, within-subject visual search procedure suggest that LI, heretofore attributed only to a deficit in the stimulus preexposed group, may, in part, be due to enhanced performance in the nonpreexposed group. Implications for the design and interpretation of LI experiments, particularly with pathologic groups are discussed.

The relation between latent inhibition and symptom-types in young schizophrenics.

Latent inhibition (LI), retarded conditioning to a stimulus that has been previously repeatedly presented without reinforcement, was examined in young schizophrenics and normal controls using a within-subject visual search task. Healthy controls exhibited the usual LI effect. LI was potentiated in schizophrenics who simultaneously exhibited high levels of negative symptoms and low levels of positive symptoms. Schizophrenic groups with other combinations of positive and negative symptoms did not differ from controls. The pattern of data suggests that past inconsistencies in the LI-schizophrenia literature may be the result of opposing processes that are associated with positive and negative symptoms.

Behavioral decrement following stimulus preexposure: effects of number of preexposures, presence of a second stimulus, and interstimulus interval in children and adults.

This article presents an analysis of the similarities between the stimulus familiarization effect and latent inhibition. Just as latent inhibition has been readily demonstrated in infrahumans, and only with considerable difficulty in adult humans, the experiments reported here obtained a significant interaction between the stimulus familiarity effect and age. Children exhibited increased reaction time to preexposed stimuli as opposed to nonpreexposed stimuli, but adults did not show this effect. In addition, a number of variables were shown to affect the amount of decrement. The decrement increased as a function of the number of preexposures and decreased with the addition of a second stimulus placed in a conditioning relationship to the to-be-tested stimulus during preexposure. However, an increased in the interstimulus interval was only marginally effective in increasing the inhibitory effects of preexposure. The data were discussed in relation to a conditioned attention explanation for these phenomena of behavioral decrement.

Latent inhibition with a response time measure from a within-subject design: effects of number of preexposures, masking task, context change, and delay.

Latent inhibition (LI), poorer performance on a learning task to a previously irrelevant stimulus than to a novel stimulus, was produced in 4 experiments, using a within-subject design and a response time (RT) measure. LI was reduced by decreasing the number of stimulus preexposures, omitting the masking task, changing the context from the preexposure to the test phase, and introducing a delay between the 2 phases. Together, these effects indicate that the within-subject RT-based LI reflects the same processes as those that govern between-subject LI with correct response as the dependent measure. The new procedure provides an advantageous method for assessing attentional dysfunction related to the processing of irrelevant stimuli, particularly in pathological groups, such as patients with schizophrenia.

The effects of target and distractor familiarity on visual search in de novo Parkinson's disease patients: latent inhibition and novel pop-out.

De novo Parkinson's disease (PD) patients identified presence or absence of a unique shape presented with homogeneous distractors. Response time (RT) was examined as a function of prior experience with target and/or distractor assessing latent inhibition (LI; slower RTs to a target that was formerly a distractor against a background of distractors that were formerly targets as compared with a novel target with distractors that were formerly targets) and novel pop-out effects. PD patients were slower than controls in detecting test-phase targets compared with preexposure-phase targets. Female PD patients with right-side motor symptoms had elevated LI compared with female controls and female PD patients with left-side symptoms. Male PD patients with right-side symptoms did not exhibit LI. Results are discussed in terms of the dopamine hypothesis and the reciprocal relationship between PD and schizophrenia.

Are high-schizotypal normal participants distractible or limited in attentional resources? A study of latent inhibition as a function of masking task load and schizotypy level.

Two experiments with normal participants examined the effects of masking and masking task load on latent inhibition (LI, poorer learning for a previously exposed irrelevant stimulus than for a novel stimulus) as a function of level of schizotypality. In Experiment 1, a masking task was needed to produce LI. In Experiment 2, with low load, LI was present in low- but not high-schizotypal participants. In high load, LI was abolished in low-schizotypal participants, but only approached significance in high-schizotypal participants. The data support a distraction- rather than a resource-limitation model of attentional dysfunction in high-schizotypal normal participants. In addition, the data indicate that obtaining LI requires that some attention be initially allocated to the preexposed stimulus and then reduced. Implications of the model for understanding attentional dysfunction in schizophrenia are discussed.