Tracking Visual Events in Time in the Absence of Time Perception: Implicit Processing at the ms Level

<div><p>Previous studies have suggested that even if subjects deem two visual stimuli less than 20 ms apart to be simultaneous, implicitly they are nonetheless distinguished in time. It is unclear, however, how information is encoded within this short timescale. We used a priming paradigm to demonstrate how successive visual stimuli are processed over time intervals of less than 20 ms. The primers were two empty square frames displayed either simultaneously or with a 17ms asynchrony. The primers were followed by the target information after a delay of 25 ms to 100 ms. The two square frames were filled in one after another with a delay of 100 ms between them, and subjects had to decide on the location of the first of the frames to be filled in. In a second version of the paradigm, only one square frame was filled in, and subjects had to decide where it was positioned. The influence of the primers is revealed through faster response times depending on the location of the first and second primers. Experiment 1 replicates earlier results, with a bias towards the side of the second primer, but only when there is a delay of 75 to 100 ms between primers and targets. The following experiments suggest this effect to be relatively independent of the task context, except for a slight effect on the time course of the biases. For the temporal order judgment task, identical results were observed when subjects have to answer to the side of the second rather than the first target, showing the effect to be independent of the hand response, and suggesting it might be related to a displacement of attention. All in all the results suggest the flow of events is followed more efficiently than suggested by explicit asynchrony judgment studies. We discuss the possible impact of these results on our understanding of the sense of time continuity.</p></div

Schematic view of the sequence of events in a single trial in the Temporal Order Judgment in Experiment 1.

<p>Primers appeared either simultaneously or asynchronously (left-right or right-left). Targets always appeared asynchronously, in either the left-right or right-left direction. The direction of primers and targets could be either congruent or non-congruent. Subjects responded by pressing the button on the same side as the first target. When the primers were asynchronous, the target stimuli appeared in either the same order as the primers (congruent condition), or the reverse order (non-congruent condition).</p

Results of Experiment 2 showing the results of the detection task with 100 ms SOA between primers and target.

<p>The graph shows the reaction times averaged over subjects for each experimental condition. For simultaneous primers, the black histogram corresponds to the condition without additional SOA (short-control condition) and the grey histogram to the condition with an additional SOA of 17 ms (long-control condition). For asynchronous primers, the black histogram corresponds to the target in the location of the second primer and the grey histogram to the target in the location of the first primer. SEMs are shown for each mean.</p

Schematic view of the luminance ramps of primers and targets.

<p>In the first task of Experiment 1, the two frames were filled in with a 100 ms onset asynchrony, such that the sequence was unambiguously perceived. Subjects were instructed to press the response button on the same side as the first square. In the second task of Experiment 1 only one frame was filled in, and subjects were told to press the button on the side of the filled-in square.</p

Results of Experiment 1.

<p>Response times averaged across subjects in the two experimental tasks: (a) temporal order judgment; (b) detection, as a function of the experimental conditions and of the primer-target SOA. SEMs are shown for each mean. For simultaneous primers, the black histograms correspond to the condition without additional SOA (short-control condition) and the grey histogram to the condition with an additional SOA of 17 ms (long-control condition). For asynchronous primers, the black histogram corresponds to the unique or first target in the location of the second primer (non-congruent condition in case of the TOJ task) and the grey histogram to the unique or first target in the location of the first primer (congruent condition in case of the TOJ task).</p

A schematic view of the sequence of events in a single trial in the detection task of Experiment 1.

<p>Primers appeared either simultaneously or asynchronously (left-right or right-left direction). A single target then appeared on the side of either the first or second primer. Subjects responded by pressing the button on the side of the target.</p

Schematic view of the SOA between the primers and the <i>first</i> target.

<p>Here we illustrate only the first (or unique) target, to show that in asynchronous conditions, the primer-first target SOA varies as a function of the location of the first target (first or second primer position).</p

Temporal Order Judgments in Schizophrenia and Bipolar Disorders – Explicit and Implicit Measures

Ordering events in time is essential for the understanding of causal relationships between successive events. Incorrect causal links can lead to false beliefs and an altered perception of reality. These symptoms belong to psychosis, which is present in schizophrenia (SZ) spectrum and bipolar (BP) disorder. Experimental results show that patients with SZ have an altered perception of temporal order, while there are no data in patients with BP. We investigated the ability of patients with SZ, BP, and controls to judge the order of stimuli with a 100-ms Stimulus Onset Asynchrony (SOA), and how such large asynchronies facilitate temporal order judgments for small asynchronies. Explicit temporal order effects suggest that patients with SZ perform worse at a long SOA (100 ms) as compared to controls, whereas patients with BP show no difference compared to controls or to patients with SZ. Implicit order effects reveal improved performances in case of identical as compared to different relative order between two successive trials for all groups, with no differences between the groups. We replicated explicit order impairments in patients with SZ compared to controls, while implicit effects appear to be preserved. This difficulty for patients to consciously order stimuli in time might be understood under the light of the loosening-of-associations phenomenon well described in SZ. Further, we showed that patients with BP do not reveal such an explicit order impairment which is consistent with phenomenological descriptions, suggesting a difference in time experience in patients with SZ and BP.</p

DataSheet1.DOCX

<p>For years, phenomenological psychiatry has proposed that distortions of the temporal structure of consciousness contribute to the abnormal experiences described before schizophrenia emerges, and may relate to basic disturbances in consciousness of the self. However, considering that temporality refers mainly to an implicit aspect of our relationship with the world, disturbances in the temporal structure of consciousness remain difficult to access. Nonetheless, previous studies have shown a correlation between self disorders and the automatic ability to expect an event in time, suggesting timing is a key issue for the psychopathology of schizophrenia. Timing disorders may represent a target for cognitive remediation, but this requires that disorders can be demonstrated at an individual level. Since cognitive impairments in patients with schizophrenia are discrete, and there is no standardized timing exploration, we focused on timing impairments suggested to be related to self disorders. We present the case report of AF, a 22 year old man suffering from schizophrenia, with no antipsychotic intake. Although AF shows few positive and negative symptoms and has a normal neurocognitive assessment, he shows a high level of disturbance of Minimal Self Disorders (SDs) (assessed with the EASE scale). Moreover, AF has a rare ability to describe his self and time difficulties. An objective assessment of timing ability (variable foreperiod task) confirmed that AF had temporal impairments similar to those previously described in patients, i.e., a preserved ability to distinguish time intervals, but a difficulty to benefit from the passage of time to expect a visual stimulus. He presents additional difficulties in benefitting from temporal cues and adapting to changes in time delays. The impairments were ample enough to yield significant effects with analyses at the individual level. Although causal relationships between subjective and objective impairments cannot be established, the results show that exploring timing deficits at the individual level is possible in patients with schizophrenia. Besides, the results are consistent with hypotheses relating minimal self disorders (SDs) to timing difficulties. They suggest that both subjective and objective timing investigations should be developed further so that their use at an individual level can be generalized in clinical practice.</p

Ultrastructure of olfactory bulb glomeruli.

<p>Electron microscopy micrographs of olfactory bulb glomeruli in WT (A) and STOP null (B–F) mice at 3 to 6 months of age. In STOP null mice, olfactory axon endings are filled with autophagic-like structures (B, arrow), tubulovesicular profiles (C, arrowhead), or both (D). When few autophagic structures were present (arrows) (E, F), olfactory axons endings could be identified by the presence of synaptic vesicles and postsynaptic densities (arrowheads) (E, F). De: dentrite; OA: olfactory axon. Scale bar: 0,5 µm (A, C, E, F); 1 µm (B, D).</p