Table 1.
List of some lines of research aimed at testing early sensory processing impairments.
| Exploration method | Some (not exhaustive) references | Targeted mechanisms | Comments |
|---|---|---|---|
| Prepulse inhibition (PPI)/accoustic startle: Reduction of the startle reflex when the stimulus inducing the startle (the pulse) is preceded by a ‘prepulse,’ i.e., a weaker sensory stimulus. The time separation between the pulse can be shorter than 100 ms. | Swerdlow et al., 2006; Li et al., 2009; Scholes and Martin-Iverson, 2010; Kohl et al., 2013; Javitt and Freedman, 2015; Morales-Muñoz et al., 2016; Vargas et al., 2016 | The inhibition of the startle reflex is supposed to be automatic, especially for short delays between prepulse and pulse (<50 ms). | – The inhibition might be under attentional control (Scholes and Martin-Iverson, 2010). |
| This inhibition is reduced in patients with schizophrenia. The results are consistent with the hypothesis of abnormal and excessive sensory responses. | – The lack of prepulse inhibition is not specific to schizophrenia (Kohl et al., 2013). | ||
| – Interestingly, the reduction of the startle reflex is more marked for intervals <100 ms in patients with schizophrenia (Swerdlow et al., 2006) and in first episode psychosis (Morales-Muñoz et al., 2016). A relationship with timing needs checking. | |||
| Sensory gating: inhibition of repeated stimuli. Two clicks are displayed with an interval of 500 ms, and the electroencephalographic response to the second stimulus is reduced relative to the first one. | Bodatsch et al., 2015; Cromwell and Atchley, 2015; Javitt and Freedman, 2015; Morales-Muñoz et al., 2016 | Like for the PPI, the inhibition of the response to the second click is reduced in patients with schizophrenia. It is likewise consistent with the hypothesis of abnormal and excessive sensory responses. | – The gating might be sensitive to cognitive and emotional influences (Cromwell and Atchley, 2015). |
| Latent inhibition (LI): The initial exposure to a stimulus prevents this stimulus to be associated with an aversive signal during a subsequent conditioning procedure. | Gray et al., 1991; Lubow, 2005; Meyer and Louilot, 2014; Vargas et al., 2016 | The conditioning is not reduced in patients. | LI might represent a model of selective attention and memory rather than of early sensory abnormalities (Lubow, 2005; Meyer and Louilot, 2014). |
| Unconscious perceptual priming: the exposure to a stimulus that is made invisible nonetheless influences the processing of a subsequent stimulus. | Del Cul et al., 2006; Jahshan et al., 2012; Kiefer et al., 2013; Langdon et al., 2013 | The unconscious perceptual priming seems to be preserved, like perceptual priming in general. | Interestingly, Kiefer et al. (2013) suggested that the time course of perceptual priming differs between patients with schizophrenia and controls. |
| Backward masking: the visibility of a visual target information is decreased by a ‘mask,’ i.e., another visual stimulus, when it is displayed right after the target information, in the location or close to the location of the target. | Saccuzzo and Braff, 1981; Green and Walker, 1986; Rund, 1993; Cadenhead et al., 1998; Butler et al., 2001; Schechter et al., 2003; Herzog et al., 2004; Tam and Liu, 2004; Koelkebeck et al., 2005; Granholm et al., 2009; Jahshan et al., 2012; Lalanne et al., 2012a | The patients with schizophrenia are more sensitive than controls to the effect of the mask and their perception of the target is altered. The explanations for the cause of this effect have been various (magnocellular deficit, reentrant processing). | – The results on unconscious priming, as well as those of Herzog et al. (2004) suggest that masking impairs access to the conscious perception of the prime, but leaves early information processing unimpaired, thus questioning whether these tasks reveal early processing impairments (Jahshan et al., 2012). |
| – The results of Granholm et al. (2009); and Lalanne et al. (2012a) suggested that impairments in masking might be related to difficulties in orienting attention in time on the target. | |||
We prioritized paradigms that have been related to sensory processing and include unconscious processing or at least implicit processing (i.e., processing that does not follow an explicit instruction). The only case including pure unconscious processing is unconscious perceptual priming. In all other cases, the information is clearly perceptible and can be consciously perceived and/or anticipated. For example, even if conditioning is a non-conscious mechanism, the fact that information leading to conditioning is perceived consciously makes it possible that the processing of conditioning information is modulated by mechanisms associated with consciousness.