DETERMINACIÓN DE LOS VALORES DE FUERZA DEBIDAS AL PANEL

conscious perception

Attention is conceptualised as a process that dynamically prioritises the

processing of certain internal models relative to others, based on expectations relating to precision of the model given its current context (Hohwy, 2012; Schröger, Kotz, & SanMiguel, 2015). This suggests attention may be the process influencing which perceptual models enter awareness at any given moment. With this in mind, the current contents of visual awareness can be defined as the prediction that is (1) accurate, that is, most probable given the previous experience and current input, and (2) currently

estimated to be most precise, namely, perceptually or motivationally salient, and therefore attended to. There may be exceptions to this, as it has been suggested that conscious perception may still be possible for states that are inaccurate but relatively precise or accurate but not very precise, a possible candidate of latter being gist perception (see Figure 1.2 for an illustration) (Hohwy, 2012). Apart from these exception states, predictive processing mechanisms suggest that a conscious percept will be the internal model that is currently most accurate (i.e., best minimises prediction error) whilst also being most precise. Although various perceptual models may be currently possible, through adjusting the gain of certain prediction error units over

others, attention may be the process that determines which models gain sensory evidence faster and thus are consciously represented.

Figure 1.2 The properties of perceptual models that enter visual awareness.

The first order statistics reflect the inverse amplitude of prediction errors, whereas the second order statistics reflect the inverse amplitude of uncertainty about predictions. The perceptual model that populates visual awareness is the one that has high accuracy (represents the visual world well) but also has high precision (is attended). This does not preclude the possibility that some conscious perceptual states may have relatively less precision but more accuracy or more precision but less accuracy. It does suggest the majority of conscious perceptual states will be both probable and attended. Image taken from Hohwy (2012).

1.3.2. Dissociation between attention and awareness

Given the proposal that attention may gate the access of perceptual models to awareness, it may be worthwhile to consider counter-evidence, as some researchers have suggested that attention and awareness can be dissociated using lab-based

manipulations, and that attention may not be sufficient or even necessary for awareness (Koch & Tsuchiya, 2007). Stimuli that are attended, whether exogenously or

endogenously, are not always consciously registered. For example, spatial attention can lead to enhanced processing of masked primes, as evidenced by the influence of cued masked primes on reaction times in a subsequent target discrimination task with congruent targets (Kentridge, Nijboer, & Heywood, 2008), despite the primes never becoming consciously visible. Additionally, spatial attention is captured by salient stimuli such as nude images that have been rendered consciously invisible by interocular suppression with high contrast noise patches, as evidenced by facilitated subsequent discrimination of visible targets presented in the same location (Jiang, Costello, Fang, Huang, & He, 2006). These examples of attentional selection and processing without awareness demonstrate that attention can be allocated to stimuli that are salient or relevant outside of awareness, and these can lead to improved processing at the associated spatial locations or unconscious priming by the relevant features. Thus, attentional allocation alone may not be sufficient for conscious perception when

masking or other highly disruptive stimuli are introduced.

Furthermore, it has been argued that top-down attention may not be necessary for the initial fast feed-forward sweep of visual processing, which results in the conscious perception of the gist of the scene, as this process occurs very quickly. In predictive processing terms this would correspond to the accurate (probable) but imprecise (not fully attended) state (Hohwy, 2012). For example, Kirchner and Thorpe (2006) found that only about 120ms are required for highly accurate semantic

categorisation of scenes. In this study two natural scenes were flashed side by side for 20ms and subjects had to report the presence of an animal by initiating a saccade to the correct side. This result suggests that the visual processing leading up to conscious detection and categorisation of objects is extremely fast, faster than the speed at which top-down attention can be initiated (i.e., about 100 – 150ms, Theeuwes et al., 2000;

Theeuwes, 2010). Selective attention may be engaged later on to prioritise the processing of particularly relevant locations or features of the extracted gist (Koch & Tsuchiya, 2007).

The necessity of attention for awareness is also called into question by

demonstrations of conscious processing and discrimination of stimuli with near absence of top-down attention in dual task paradigms. Here, discrimination between categories of briefly peripherally presented scenes (e.g., animal present or absent, vehicle present or absent) is still possible when engaging top-down attention in a demanding central task (Li, VanRullen, Koch, & Perona, 2002). Crucially, the accuracy of categorisation is unchanged relative to single task conditions and performance in the central task does not decrease due to the peripheral categorisation. This effect is also present when discriminating between peripherally presented male and female faces in a dual task paradigm, although performance is impaired when categorising computationally easier but ecologically less important stimuli such as green-red or red-green discs (Reddy, Wilken, & Koch, 2004). Together these results seem to indicate that attention may not be required for the initial steps of building a conscious representation of the natural visual scene and extracting its semantic meaning.

However, after a closer consideration of this evidence, it is questionable whether awareness and attention truly dissociate under natural continuous conscious perception of the visual world. It must be noted that in lab-based studies where attended stimuli do not become consciously visible, some manipulation is typically present to prevent the stimuli from entering awareness, such as masking (Kentridge et al., 2008) or interocular suppression (Jiang et al., 2006). Under these conditions, although precision may be initially allocated to the subliminal stimulus, it is then disrupted or masked by a salient distractor. Thus, what these paradigms show is that subsequent performance can benefit

from spatial or feature-based allocation attention even if attentional processing is disrupted by masking and therefore does not lead to awareness. Similarly, it is arguable whether a central task that requires focal attention in dual-task paradigms completely exhausts attentional resources (e.g., covert attention) (Li et al., 2002; Reddy et al., 2004), especially if it is not perceptually complex (Lavie, 1995). The task instruction to detect faces may, for example, serve as an attentional set that increases precision or baseline activity of face representations giving them competitive advantage even when focal attention is engaged in the central task.

It would also be helpful to ascertain whether pre-attentive visual processing, as in the case of fast peripheral presentations under dual task conditions, can lead to a rich conscious experience of the scene to be able to claim visual processing with minimal or absent attentional resources still leads to conscious perception. The initial fast feed- forward sweep of visual processing terminates at high-level cortical areas that have large receptive fields and code abstract, position and viewpoint invariant object representations (Campana & Tallon-Baudry, 2013). This leaves us with a vivid representation in the sense that semantic content of the scene is extracted but the representation is coarse in that consciously it only provides us with the experience of gist. Detailed perception follows from cortical re-current feedback to low-level areas and attentional selection of particular representations for amplification of signal and thus more focused processing (Lamme, 2003). It is questionable whether the gist perception that it sufficient for simple semantic categorisation could sustain conscious awareness if it was not followed-up by cortical feedback mechanisms and selective attentional processing. In fact, disruption of re-current processing typically impairs awareness (Lamme, 2003). Therefore, although attention and awareness can be

dissociated in the lab, the argument that attention is not necessary for conscious detection of visual stimuli is not convincing.

1.3.3 Summary

The debate sketched out here largely corresponds to the division of awareness into phenomenal and access consciousness, whereby the former is described as the phenomenal experience of perceptual content but the latter is defined as the part of this experience accessible for memory, planning, reasoning, and decision-making systems, as well as voluntary action and introspective report (Block, 2005; 2011). The key distinction here is that what is available for phenomenal awareness may not always be possible to access and report, as phenomenal representations are thought to compete for access to the planning and output systems. Although phenomenal awareness or a

percept of a gist may be generated very quickly and possibly in the near absence of attention (Kirchner & Thorpe, 2006; Li et al., 2002; Campana & Tallon-Baudry, 2013), it is unclear if such representations could support conscious detection of visual change. The representations available for phenomenal awareness may be subserved by a

temporally fragile but rich stage of visual STM, which then contributes to the more accessible and robust but limited capacity VSTM (Lamme, 2003; Sligte, Scholte, & Lamme, 2008; Sligte, Scholte, & Lamme, 2009). Attention may be the cognitive

process that determines which contents of phenomenal awareness become accessible for report. This thesis aims to investigate visual change detection and therefore this type of process likely requires access consciousness. Although phenomenal awareness can be supported in the near absence of attention, attention may be necessary in order to become aware of visual stimuli and be able to report them.

1.4. Predictive processing biases and individual